geoinformatics 2007 vol06

45
Coming Soon: GeoEye’s Next-Generation Color Satel In the months ahead a commercial Earth imaging satellite, GeoEye-1, will be launched by GeoEye Inc. It will provide the highest resolution and most advanced collection capabilities of any commercial remote sensing system. The satellite will acquire high-quality panchromatic and multispectral imagery at spatial resolutions of 0.41-meters in the panchromatic mode and 1.64-meters in the multispectral mode, respectively, and collect hundreds of thousands of square kilometers of map-accurate imagery in a single day. By Kevin Corbley As a comparison, GeoEye-1 will be much larg- er than IKONOS, the world's first high-resolu- tion commercial imaging satellite launched in 1999 by then Space Imaging. GeoEye was formed in January 2006 when Orbimage pur- chased the assets of Colorado-based Space Imaging. The newly formed company is now known as GeoEye and its headquarters is in the Washington D.C. area. The IKONOS satellite weighs 1,600 pounds, while GeoEye-1 will tip the scales at more than 4,000 pounds, collec- ting imagery as it moves 425 miles (684 kilo- meters) above the earth at about 17,000 miles per hour. A Team of Partners To bring about such a major endeavor, GeoEye president and CEO Matthew O'Connell assem- bled a team of partners to develop and launch GeoEye-1. Gilbert, Arizona-based General Dynamics/Advanced Information Systems serves as the prime contractor and integrator for the satellite's bus and telescope. To develop a camera capable of acquiring imagery at 41-cen- timeter spatial resolution (16 inches), GeoEye turned to ITT, formerly Kodak Remote Sensing Systems, which also built the IKONOS sensor. The satellite will be lifted into orbit on a Boeing Delta II launch vehicle from Vandenberg Air Force Base in California. Following the launch of GeoEye-1, the satellite will undergo about 45-60 days of calibration and checkout. Once the satellite is declared operational, it will begin a three-month imaging operation mostly dedicated to meeting the needs of the Pentagon’s National Geospatial-Intelligence Agency (NGA). For the most part, imagery collected during this period will also be made available in the company archive for commercial sale. GeoEye will take commercial orders during this timeframe and fulfil them as soon as possible. While GeoEye-1 will be able to collect imagery at 41-centimeter ground resolution, imagery for commercial customers will be re-sampled to half meter resolution before sale. This is due to current U.S. government licensing restrictions. However, GeoEye is seeking a waiver to their license in order to be able to provide the highest resolution imagery to governmental customers in some countries. For example, in the European region, GeoEye has requested that Poland be able to have direct access to GeoEye- 1 and governmental customers there be able to utilize 41-centimeter imagery. On June 29, 2007, the National Oceanic and Atmospheric Administration (NOAA) notified all U.S. commercial imagery providers that the 24 hours hold rule for imagery better than the res- olution of the IKONOS satellite (.82-meter) has been lifted. This licensing restriction was originally created early in the history of the September 2007 6 Interview GeoEye-1, shown here in an artist’s rendering, will offer the highest resolution and most advanced collection capabilities of any commercial imaging satellite.

Upload: protogeografo

Post on 26-Nov-2015

69 views

Category:

Documents


0 download

DESCRIPTION

geoinformatics 2007 vol06

TRANSCRIPT

  • Coming Soon:

    GeoEyes Next-Generation Color Satel

    In the months ahead a commercial Earth imaging satellite, GeoEye-1, will be launched by GeoEye Inc. It will provide the

    highest resolution and most advanced collection capabilities of any commercial remote sensing system. The satellite will

    acquire high-quality panchromatic and multispectral imagery at spatial resolutions of 0.41-meters in the panchromatic

    mode and 1.64-meters in the multispectral mode, respectively, and collect hundreds of thousands of square kilometers of

    map-accurate imagery in a single day.

    By Kevin Corbley

    As a comparison, GeoEye-1 will be much larg-er than IKONOS, the world's first high-resolu-tion commercial imaging satellite launched in1999 by then Space Imaging. GeoEye wasformed in January 2006 when Orbimage pur-chased the assets of Colorado-based SpaceImaging. The newly formed company is nowknown as GeoEye and its headquarters is in theWashington D.C. area. The IKONOS satelliteweighs 1,600 pounds, while GeoEye-1 will tipthe scales at more than 4,000 pounds, collec -ting imagery as it moves 425 miles (684 kilo-meters) above the earth at about 17,000 milesper hour.

    A Team of PartnersTo bring about such a major endeavor, GeoEyepresident and CEO Matthew O'Connell assem-bled a team of partners to develop and launchGeoEye-1. Gilbert, Arizona-based GeneralDynamics/Advanced Information Systems serves

    as the prime contractor and integrator for thesatellite's bus and telescope. To develop a camera capable of acquiring imagery at 41-cen-timeter spatial resolution (16 inches), GeoEyeturned to ITT, formerly Kodak Remote SensingSystems, which also built the IKONOS sensor.The satellite will be lifted into orbit on a BoeingDelta II launch vehicle from Vandenberg AirForce Base in California.Following the launch of GeoEye-1, the satellitewill undergo about 45-60 days of calibrationand checkout. Once the satellite is declaredoperational, it will begin a three-month imaging operation mostly dedicated to meeting the needs of the Pentagons NationalGeospatial-Intelligence Agency (NGA). For themost part, imagery collected during this periodwill also be made available in the companyarchive for commercial sale. GeoEye will takecommercial orders during this timeframe andfulfil them as soon as possible.

    While GeoEye-1 will be able to collect imageryat 41-centimeter ground resolution, imagery forcommercial customers will be re-sampled to halfmeter resolution before sale. This is due to current U.S. government licensing restrictions.However, GeoEye is seeking a waiver to theirlicense in order to be able to provide the highest resolution imagery to governmental customers in some countries. For example, inthe European region, GeoEye has requested thatPoland be able to have direct access to GeoEye-1 and governmental customers there be able toutilize 41-centimeter imagery.

    On June 29, 2007, the National Oceanic andAtmospheric Administration (NOAA) notified allU.S. commercial imagery providers that the 24hours hold rule for imagery better than the res-olution of the IKONOS satellite (.82-meter) hasbeen lifted. This licensing restriction was originally created early in the history of the

    September 20076

    Interv iew

    GeoEye-1, shown here in an artists rendering,

    will offer the highest resolution and most

    advanced collection capabilities of any

    commercial imaging satellite.

    Prod_GEO_6_2007:Prod GEO66 24-08-2007 13:59 Pagina 6

  • commercial remote sensing industry. This willenable space-based commercial imageryproviders to sell imagery from current and nextgeneration satellites immediately upon collec-tion.

    Mapping in OrbitThe GeoEye-1 satellite fundamentally will be amapping machine in orbit, explains MarkBrender, GeoEye's vice president of communi-cations and marketing. We will be able to offercommercial customers half-meter resolutioncolor imagery with the most accurate geo-location accuracy ever achieved in a com mercialspace-based system, he said. GeoEye recently acquired M.J. Harden, an aerialimaging and geospatial firm in Mission, Kansas.The firm flies two aircraft, one with a digitalmapping camera, and the other with a newLiDAR imaging system. The combination ofaerial and satellite imagery will be a powerful

    meter multi-spectral in theblue, green, red, and near-infrared bands, the satellitewill enable clients to identifysmall objects and features ata level of detail never avail-able before from commercialimaging satellites. At thatresolution, you can count themanholes on a city street ordiscern home plate on abaseball diamond. Geo -spatial data users in thedefense and intelligence, oiland gas, insurance, urbanplanning, utility, and carto-graphic disciplines- all ofwhich traditionally map small

    features-are expected to expand their use ofsatellite imagery as a result.It's anticipated that online search engines suchas Yahoo!, Google Earth, and Microsoft VirtualEarth also will be anxious to import consistenthigh resolution color imagery over large areas.In addition, though satellite and aerial imagesoften are complementary, GeoEye expects manytraditional users of aerial imagery to jump tosatellites for applications requiring half-meterresolution, especially in parts of the worldwhere it's difficult to deploy an aircraft due toweather, political, or security issues.But there's more to good imagery than spatialresolution, notes Lee Demitry, GeoEye's vicepresident of engineering. People are going tobe stunned with the sharpness and clarity ofthis imagery, he predicts, explaining that overall image quality, most often defined by thesharpness of feature boundaries, is just as critical as spatial resolution to many applica-tions. The camera builder, ITT, has employednew technological advancements to achieve thislevel of image quality. The large size of thetelescope's primary mirror, the alignment of thecamera telescope, and a favorable (high) signal-to-noise ratio are key design elements inultimately producing high-quality imagery.Geo-location accuracy is another imaging capability GeoEye expects will appeal to endusers across all market segments. This refers tothe precision with which objects in an imagecan be mapped relative to their absolute location on earth's surface. GeoEye-1 will offerthree-meter accuracy, which means end userscan map natural and manmade features in

    tool for mapping and surveying, Brender said.In June of this year GeoEye invested in a privately held company called Spadac. Spadacutilizes geospatial technologies in doing predictive analytics. GeoEye is working closelywith Spadac in offering customers the tools tohelp them take pixels to the next level. SaysBrender, Spadac helps us extract knowledgefrom our pixels and aids our customers in better understanding issues before they becomeproblems.

    Advanced CapabilitiesAs a major customer, NGA will receive prioritytasking and a substantial discount for agreeingto purchase a large volume of imagery. Butample capacity will be dedicated to commercialcustomers and allow the company to build avast archive of imagery in relatively short time.Spatial resolution, geo-location accuracy, andlarge-area coverage are the three specificationscommercial and government customers aremost interested in, says Dave Kenyon, GeoEyesenior director, space segment engineering.And those are the key capabilities we focusedon when building this satellite. Of course, res-olution is the parameter by which most judgeand compare imaging satellites. Frank Koester, vice president and director,Commercial and Space Science Program, ITTSpace Systems Division, says, ITT's integratedcamera payload, including telescope and sensor subsystem, will provide GeoEye-1 withthe highest resolution in commercial remotesensing.Offering 41-centimeter panchromatic and 1.64-

    September 2007Latest News? Visit www.geoinformatics.com 7

    Interv iew

    l lite Imagery

    Once launched GeoEye-1 will be equipped with themost advanced technology ever used in a commercialremote sensing system. The satellite will be able tocollect images at 0.41-meter panchromatic (black &white) and 1.65-meter multispectral resolution. Asshown in the following simulation using IKONOSsatellite imagery (a) and aerial photography (b), thedetailed half-meter imagery will expand the applica-tions for satellite imagery in every commercial andgovernment market.

    [a] [b]

    Prod_GEO_6_2007:Prod GEO66 24-08-2007 13:59 Pagina 7

  • stereo to within three meters of their actuallocations without ground control points.This level of geo-location accuracy will beachieved with the help of three onboard systems: a GPS receiver, gyroscope, and startracker, which will enable the satellite to deter-mine its precise attitude, position, and locationat all times. Such ancillary data will be trans-mitted along with image data back to earth forthe ground segment to use in processing theimagery. Some of these systems, such as thestar tracker, have never flown on commercialsatellites before and were only used on U.S.government imaging satellites. Adds Demitry,The ability to map features with this level ofhorizontal accuracy without any ground controlis for commercial satellites and will be a hugeadvantage- and enormous cost savings-for anycartographic application.

    Prodigious ImageryThe third major technological advancement foundin the GeoEye-1 satellite will be its ability to collect an enormous amount of imagery. In thepanchromatic mode, the satellite will be capableof collecting up to 700,000 square kilometers ina single day and in the multispectral mode350,000 square kilometers per day. This volumeof data collection-more than four times that ofany other existing commercial imaging platform-will be made possible by the agility of the satel-lite itself. The entire satellite will be able to turnand swivel quickly in orbit to point the cameratelescope at areas of the Earth directly below it,as well as from side to side and front to back,explains GeoEye's Kenyon. This agility willenable it to collect much more imagery during asingle pass.According to Mike Greenwood, spokesperson forGeneral Dynamics Advanced InformationSystems, the agility is made possible byenhanced reaction wheels that provide thetorque required for motion yet inject little jitteror smear into the imagery. The standard imageswath width will be 15.2 kilometers, but GeoEye-1 will be able to swivel and collect multipleadjoining swaths on a single pass, meaning thatvery large contiguous areas can be imaged at onetime. This is ideal for large-scale mapping require-ments, especially for emergency response anddisaster relief. The agility also means GeoEye cansatisfy more than one client during a single passby collecting a variety of individual scenes in thesame geographic region. The satellite will swivelup to 40 degrees off nadir, giving it an effectiverevisit rate of less than three days.GeoEye has already announced plans to put thelarge-area imaging capability to work in filling itsarchive. The company says it will collect as muchland imagery as possible on every pass and storeit in the archive whether there is a tasking orderfor the scenes or not.

    Defense and IntelligenceFor government applications, especially thoseinvolving the defense and intelligence commu-nities, the large-area coverage combined withthe 41-centimeter spatial resolution has spurredthe greatest anticipation for the new satellite,according to Jim Lewis, director of theTechnology and Public Policy Program at theCenter for Strategic and International Studies(CSIS) in Washington, D.C. Lewis says GeoEye-1will help take pressure off U.S. Department ofDefense satellites because it will provide datafor many of their applications, partly becauseits spatial resolution and coverage area mayapproach the same capabilities as classifiedimaging systems. In the defense/intelligencecommunity, you have competition for assets, sothey have to prioritize which mission comesfirst, he explains. Being able to go outsidethose government assets and get a commercialsystem that can provide you things on a muchfaster basis can only help. And the governmentrides on the investment made by Wall Street incommercial remote sensing. Lewis adds that commercial imaging systemsreceive tremendous support from the U.S.Department of Defense because their imagesaren't classified. Although this may sound coun-terintuitive, military agencies often favor unclas-sified information, including satellite imagery,because it can be shared more freely with alliesand coalition partners or nongovernmentalorganizations. Security concerns aren't an issuewith commercial satellite imagery.Under the development expertise of GeoEye andits key suppliers, the company has upgraded acentralized command and control facility at itsheadquarters in Dulles, Virginia. This operationscenter will send tasking and operating com-mands to the satellite and receive data down-links from it. Three other stations will be oper-ated or leased by GeoEye in Alaska, Norway, andAntarctica. Regardless of location, GeoEye-1 cus-tomers will be able to see what's available forsale easily. The company recently enhanced itsexisting archive search tool, known asImageSearch, to allow clients to perform onlinesearches of the IKONOS archive. They expect tobe able to deliver images to a client shortlyafter collection by the satellite.That scenario should come soon, as theGeoEye-1 team anxiously anticipates the launchof its satellite that should expand the reachesof satellite imagery and remote sensing for thegovernment, commercial customers, and thepublic.

    Kevin Corbley is a principal with Corbley

    Communications in Winchester, Virgina. Graphic

    illustration and images courtesy of GeoEye. For more

    information on this subject visit www.geoeye.com.

    Announcement of GeoEye-1's imaging specifica-tions has elicited responses from both the commercial and private-sector imagery markets.Ed Jurkevics, a remote sensing industry consul-tant and principal analyst at ChesapeakeAnalytics in Arlington, Virginia, singles out thelarge-area imaging. GeoEye-1 will be able todeliver imagery over large areas in a relativelyshort and reasonable time. So clients can expectto receive a complete image map over a largearea such as a country in one season rather thanover many months, he said. This will be espe-cially important for EU countries in mapping outagricultural yields and measuring the size of landparcels, added Jurkevics.He explained that for large-area mapping projects, fast acquisition improves the overallsuccess. If too much time elapses between collections of contiguous scenes, for example,changes in ground conditions such as vegetativegrowth or soil moisture can adversely impact cor-relations made among the scenes. The accuracyof digital elevation model extraction from imagepairs can degrade if the image pairs were col-lected at different times under different condi-tions.

    September 2007Latest News? Visit www.geoinformatics.com 9

    Interv iew

    As shown in this simulation using IKONOS satelliteimagery (a) and aerial photography (b), the half-

    meter imagery will even be able to discern home plateon a baseball diamond.

    Prod_GEO_6_2007:Prod GEO66 24-08-2007 13:59 Pagina 9

  • applications in the web. In fact, the potentiallegal liabilities I was talking about are anindustry-wide issue, which to my knowledgehas not yet been adequately addressed.

    My main concern is that providers of softwareand data typically are not required to warranttheir products, and frequently provide dis-claimers which essentially amount to buyerbeware. But the problem is that it is nolonger practical to think such disclaimers cancontinue to make suppliers or their customersinvulnerable to liability in cases involving seri-ous consequences. This is all complicated ofcourse by the many ways in which value canbe added to spatial data. The OGCs GeoRights Management Working Group and DataQuality Working Group will bear in positiveways on this problem, but there is nopanacea, and it would be good to see widerdiscussion of the issue. In a very real sense,we are all in this together. If I did indeed referto all hell breaking loose over this issue Iwould not have been referring to myself or tothe consortium I would most definitely bereferring to the much greater visibility of spa-tial data as mapping enters the IT mainstream,and the fact that standards of usage and bestpractices which have traditionally been under-stood between suppliers and users will almostcertainly become less clearly understood withthe result that the quality of both data andspatial services will become less professionaland perhaps less reliable.

    Another issue I know you want to clarifyconcerns the relation of Googles KML toOGCs standard for GML. Google haspositioned KML to be a major enabler ofpopular mapping on the Web, andGoogle has recently joined the OGC.Could you comment on the meaning ofthis relationship and on the future ofKML and GML in general?

    Yes, I think the OGC-Google relationship isvery important, and there is no question thatwe share an interest in creating a coherentand productive standards environment forinformation and application interoperabilitythat provides a basis for industry-wide shar-ing of geospatial information. The issue I havewith the phrasing in the article is that I didnot say, We better integrate GML with KML.

    David Schell Speaks

    Open Geospatial Consortium

    As a founder of the OpenGIS Foundation (OGF), the OpenGIS Project,

    and the Open GIS Consortium, later re-christened the Open Geospatial

    Consortium (OGC), David Schell is a true visionary and a pioneer in

    the work field of spatial information.

    By Remco Takken

    Art ic le

    David Schell: it is inevitable thatsituations will arise where some-ones naive confidence in widelyused but uncertified or informallycompiled data results in loss of lifeor property.

    I am glad we have this opportunity todiscuss the current state of our industry.I understand you would like to clarifysome issues that were mentioned in the1Spatial article we published inGeoInformatics 5-2007. I think you feelthat some of the complex issues youraised were not precisely stated andneed some additional explanation.Maybe that's where we should start.

    I, too, am very glad we have a chance to dothis interview. Yes, I would like take thisopportunity to clarify some of the statementsthat were attributed to me in the coverage ofmy 1Spatial speech in your last issue. Imafraid that in trying to summarize what I saidfor the article many of my ideas were reducedto one-liners that did not do justice to the

    complex issues I discussed and I want to cor-rect any possible impression that what I saidwas meant to be critical or confrontational.

    The article, for example, mentioned yourconcern with the issue of liabilitiesthat could arise from the use of spatialinformation. Could you explain what youmean by liabilities and what sort ofproblems you had in mind?

    Yes. My meaning concerned the growing pop-ular use of spatial data and online maps --that it is inevitable that situations will arisewhere someone's naive confidence in widelyused but uncertified or informally compileddata results in loss of life or property. Whenpeople develop and publish such maps in aninformal, ad hoc, almost conversational fash-ion, they are most of the time not thinkingof this. Publishers of map data, both recre-ational and professional, are finding theirmarkets growing rapidly, and some customersare using that data not only for entertainmentactivities but for serious planning, assumingthat the data can be fit for purpose andtotally reliable, even if the data is not intend-ed nor tested by a credible authority for lifecritical projects.

    I was surprised that the conclusion of the arti-cle seemed to suggest that I am concernedonly about the part played by OGC standardsin this regard referring of course to the factthat interoperability standards play a part in

    preserving the reliability of data across

    September 200710

    Prod_GEO_6_2007:Prod GEO66 24-08-2007 14:00 Pagina 10

  • Integrate is the wrong word to use here its not a question of integration. The prop-er word is harmonization. And I am not inthe habit of dictating to the members. I didsay that Google has joined the OGC and weare pleased with that, and we have - almosteveryone has - an interest in the harmo-nization of these specifications for the pur-pose of developing efficient and consistentmarket practices. The two encodings arelargely complementary, so we dont expectmajor difficulties. But the requirement toharmonize such specifications is entirely amember issue. I think it would be a goodthing but I am entirely ready for the mar-ket to do what the key players think is best.Oh, and in relation to this it was stated thatMicrosoft had joined OGC when in fact mycomment related to our discussions withMicrosoft concerning their obvious interestin this issue, as they are very likely to wishto participate in the harmonization process toensure an industry-wide standard of this sort.

    I believe you did say that you were concerned that the industry was movingso fast.

    Different companies naturally tend to putforward different technology approaches forprofit, and we all know that profit doesntalways wait for an orderly standards pro-cess, so stovepiping develops. Our presentsituation presents challenges, the kind ofchallenges that it has taken us 15 years toovercome in evolving the GIS market fromits proprietary business models to partici-pation in an open environment of Web ser-vices. Im not at all pessimistic, but I thinkthat one of our greatest challenges is tomotivate technology users and providers tobe concerned enough about this issue tostay engaged in the standards process, nomatter how long it takes to deal with theaccelerated change we are experiencing.With the new wave of consumer mappingcoming into the market characterized bylightweight processes, different objectives

    and a focus on advertising and consumerissues we face the challenge of integratinga new style of development and geospatialprocessing into a thirty year tradition of ahighly focused and intricate technologyshared by the major GIS companies as wellas the research establishment. The concern Iexpressed actually dealt with the requirement

    Thats true. When the market is developingvery fast when it is exploding as it is nowwith thousands of new developers and mil-lions of consumers, theres a danger thatbecause of commercial pressures there wontbe enough time to develop standards beforethe market is populated again with non-inter-operable products.

    September 2007Latest News? Visit www.geoinformatics.com 11

    Art ic le

    some customers are using that data not only for entertain-ment activities but for serious planning...

    Prod_GEO_6_2007:Prod GEO66 24-08-2007 14:00 Pagina 11

  • for building on the richness of that traditionin creating the new environment oflightweight spatial processes which character-ize the new markets a concern that I linkback to the issue of liability and the need forpeople to be able to rely on the accuracy oftheir data products. There are two differentcultures to consider which are now character-ized on the one hand by traditional GIS pro-fessionals and on the other by fast-movingmashup enthusiasts. The challenge for theConsortium is to embrace and help enable thenew style of development while maintainingthe value thats already been produced.

    You referred to the GIS market as aboutique market?

    The GIS market was, in its beginning, a rela-tively small, specialized market for a very par-ticular group of application developers andresearchers that had not yet come into the ITmainstream this sort of market is often, andnon-prejudicially, called a boutique market.The point is that todays market for geospa-tial information is not the sort of specialtymarket that it was in the 80s, when spatialinformation was only accessible by means ofproprietary commercial applications or by gov-ernment and university research laboratories.Now we have the Internet, and a much largerworld-wide market of open resources. Ofcourse the pioneers of the geospatial fieldcharacterized and promoted the market in thebeginning. Its in the nature of things no mat-ter what you call it, and it was a closed mar-ket. The point is that we now live in a worldof open standards and active sharing of ser-vices and data one that is getting to be solarge and diverse that it definitely no longerserves just the needs of a few specialty shop-pers.

    So, looking forward now and taking awider view of things, what would yousay will be the main purpose of the OGCas we look at the future of geoproces -sing in general?

    The OGC serves as a clearinghouse, or anorganisational backbone for those interestedin geographic information. Its primary raisondtre is to ensure that spatial informationis used freely. By that I dont mean without

    it impossible for GI and its various data typesto be used more generally both to grow ahealthy and robust business community andto improve conditions for the benefit ofmankind. The non-interoperability that wasperpetuated by this situation contributed sig-nificantly to societys lack of preparedness forgetting and delivering the full benefit of spa-tial information in dealing with such criticallife threatening issues as climate change, dis-aster preparedness, and agricultural develop-ment. For years it was non-interoperabilitythat was the reason for the artificially highprice for spatial data and services, and theresulting high cost of building complex sys-tems that require efficient accessibility andusability of spatial information.

    What are your views on national govern-ments role in providing geospatial data?

    If the OGC has done one thing to be proudof, it has been the democratisation of the spa-tial information process. The OGC has pro-moted the creation of an open market pro-cess that prevents the growth of limiting,monopolistic tendencies involving some ofthe most vital data on which peoples livesdepend.

    Some kinds of data and information shouldbe funded by the public sector, because theyare so fundamental to public issues and thewelfare of mankind. And I do think, to adegree, that spatial data should be looked atas a necessary commodity, like water. Theressuch a great dependency on it. The creationand maintenance of spatial informationshould be viewed by governments as thesame kind of investment as any other infras-tructure on which people depend, like anyother government service which is providedfor the safety and the welfare of its citizensas a result of informed policy making.

    pay, but in a barrier free,easy, accessible way inthe IT-community.

    Actually, although fromme it may seem like acontradiction in terms, itmay be best not toemphasize standardsdevelopment exclusivelywhen talking about thework of the OGC. Ourgoal is not just makingstandards, but to helpcreate successful busi-ness models that makethe use of geospatialinformation ubiquitous. Clearly the standardsthat we develop are a key component of get-ting to a successful business model. But stan-dards are transitory; they change with theevolution of technology. It is much better torefer to OGC as an organization dedicated tothe reconciliation of user requirements withthe development community standards arethe vehicle for ensuring that the two cooper-ate and work together efficiently.

    In fact, a key reason for the existence of theOGC is to provide a forum in which competi-tive organisations that have a very significantinterest in the development of the geospatialmarket can meet and discuss issues thataffect the user community. They have theopportunity, in a civilized and socially respon-sible context, to develop norms of behaviourand best practices, governing all uses of spa-tial information in a responsible way-a waythat serves the public interest.

    You have spoken in the past of demys-tifying GIS. What does that mean andwhy is it important?

    Thats right. We want to demystify GIS. Wewant people to understand that informationabout space or location is a necessary dimen-sion of any kind of information processing.Its very unfortunate that for so many yearsthere was resistance to breaking down thebarriers around the GIS market. For a longtime, the GIS market seemed to enforce theidea that there is an exclusive relationshipbetween data type and application. This made

    September 2007Latest News? Visit www.geoinformatics.com 13

    Art ic le

    We want to demystify GIS.

    I think the OGC-Google relationship is very important, and there

    is no question that we share an interest in creating a coherent

    and productive standards environment for information

    and application interoperability...

    Prod_GEO_6_2007:Prod GEO66 24-08-2007 14:00 Pagina 13

  • Do you think that governments are nowin general meeting this challenge?

    In many cases, commercial opportunism andthe lack of good government policy regardingthese issues have prevented an appropriateassessment of the infrastructure value of spa-tial information services, and this has donean injustice to people around the world. Theresult of this condition is that there is exten-sive disagreement about the state of theworlds natural resources and climate, and adangerously inadequate capability to assessmuch of the worlds aging built infrastructure.With poor geospatial information its difficultfor policymakers to come to an agreement onsolutions regarding maintaining a well-ordered society, which could otherwise beobvious.

    But with INSPIRE and other programs,dont you find that this is changing?

    Yes, the situation does seem to be improv-ing. But geographic information resources arestill, in my opinion, generally under-funded bygovernment, although more policymakers arebeginning to take notice of the requirementfor abundant, easily discovered, easily evalu-ated, easily accessible, and easily usedgeospatial information. The Web has beenvery helpful in forcing the review and mod-ernization of information systems in govern-ment agencies around the world, and the ideaof loosely coupled open systems has gained

    widespread acceptance. Such systems require,by definition, that subsystems connectthrough open interfaces. And this, of course, iswhat the OGC has been demonstrating formore than ten years with surprising success.In Europe, INSPIRE calls for the use of OGCstandards. The Canadian Geospatial DataInfrastructure, a program shared by multipleagencies, is based on OGC standards through-out. In Great Britain, the Ordnance SurveysOS MasterMap supports distribution as GML.The US Census lists TigerGML as a futureCensus Bureau product, the US national dataportal (The National Map) is based on OGCstandards, and OGC standards are written intothe US Federal Enterprise Architecture. There iswidespread adoption of OGC standards inAustralia. GML is specified in electronic-Government Interoperability Framework (e-GIF) best practices in the UK, New Zealand,Denmark and Hong Kong. There are many oth-ers, and the list keeps growing.

    You began by speaking about new anddifficult challenges in the industry. Whatwould be the role of universities inmeeting these challenges?

    I think its incredibly important. Now thatinformation about space and time is easilyprovided as a dimension of any kind of infor-mation processing, we are on the verge ofsomething truly exciting. Building on rapidadvances in bandwidth, CPU speed, miniatur-ization and storage capacity, extraordinary

    things are happening. You see it in consumerdevices like the iPod, in Web services, inonline virtual reality games and in all sorts ofplaces. The issue for academia is to under-stand and lead the convergence of these tech-nologies with spatial technologies.

    In my view, this should be seen as a new sci-ence. The rapidly emerging convergence ofmodeling, semantics, high performance com-puting and geospatial technologies is deliver-ing new modes of understanding and inquirythat need to be codified and brought togeth-er in a supportive academic environment.Without a concerted global effort of this sort,we will miss the opportunity for the fullestpossible use of geospatial data and servicesin the rapidly evolving ICT environment.

    Doesnt the OGC provide such a support-ive environment?

    Standards developers must, by definition,seek common denominator approaches,approaches that are as simple as possiblefor good practical reasons. However, this goalfrequently runs counter to the need to havestandards that are as complex as necessaryto maintain rigor in scientific specialties. Theworld faces difficult challenges that dependon science and decision support being radi-cally empowered by information and commu-nication technologies that have a full measureof spatial enablement. The standards world,the commercial world and the academic worldneed to work together to make this so.

    Thank you. Weve covered a lot ofground today! I look forward to our nextinterview.

    Youre welcome. Thank you for the opportu nityto bring these issues to your readers.

    Remco Takken ([email protected]) is an

    editor at GeoInformatics. More information about the

    OGC can be found on www.opengeospatial.org.

    September 200714

    Art ic le

    I think the OGC-Google relationship is very important.

    Prod_GEO_6_2007:Prod GEO66 24-08-2007 14:00 Pagina 14

  • RTK to the Limit

    Multi-test UHF RTK setsRTK systems are commonly used in land surveying, hydrographic surveying and

    machine control. While the first is switching more and more to GSM telemetry such

    as NTRIP, the last two almost completely depend on UHF radio for telemetry of the

    correction signal. For this review we selected five UHF RTK dGPS systems

    commonly used in the land survey and/or machine control industries.

    By Huibert-Jan Lekkerkerk

    The reviewed systems are: Leica Geosystems GX1230GG Smartrover

    (Leica) Magellan Professional Z-Max (Magellan) Sokkia GSR2700 ISX (Sokkia) Topcon GR-3 (Topcon) Trimble R6 GNSS (Trimble)

    All systems were tested in the configurationdelivered by the Dutch or European reselleror representative, including the recommend-ed controller and software packages. All wererequested to include a UHF radio capable oftransmitting and receiving correction signalson a permit-free frequency and power settingfor the Netherlands.

    Test MethodIn contrast with other reviews I have per-formed, I tried to test some of the more objec-

    tive specifications of the equipment. Theproblem with performing tests, though, is thatas an editor I cannot afford a highly sophisti-cated laboratory. InsteadI performed the tests inthe field and at homeusing either the re ceiversthemselves or simpletools that everyone haslying around the homeor workshop.The tests performedincluded a range test, re-initialization tests,weight and volume testsas well as a limited pre-cision test and en du -rance test. In order to beable to compare theresults, all tests had to

    be taken under the same circumstances (as faras possible in the field).Besides these specialized tests I performed amore regular review as well, concentrating onuser friendliness. The latter was evaluatedduring the field tests and no specific surveywas performed. The total test time for eachsystem depended on the maximum enduranceof the rover and varied from 6.5 hours (Leica)to 14.5 hours (Magellan).This review is divided into two parts: the tableand main text describe the results of the moreobjective tests and comparisons, while thecadres detail the results of the practical tests,including user friendliness.

    September 200716

    Review

    Reviewed systems set up on dike.

    Cases, tripods and poles as delivered.

    Prod_GEO_6_2007:Prod GEO66 24-08-2007 14:00 Pagina 16

  • September 2007Latest News? Visit www.geoinformatics.com 17

    Review

    System Description

    Leica GX1230 GGThe base station tested has a different set-upfrom the rover and uses a separate geodeticantenna, receiver and correction transmitter.As a result the base is rather bulky althoughnot exceptionally heavy. The connectionbetween base receiver and antennas is madeusing identical cables which can be prone toswitching. The differential antenna arm onboth rover and base can be clipped to thereceiver so that it either points up or down, depending on the userrequirements. The rover receiver is very light at 1.2 kilograms although this is compen-sated by the weight of the controller and separate correction receiver.The rover battery is relatively small and does not last through a full survey day. Due to its different layout the base station has just enoughendurance for a full survey day. For the base a separate battery packwas supplied which extends the endurance by roughly 16 hours, althoughthis pack was not used during the tests.The Bluetooth connection between rover and controller functioned without noticeable problems. Since both base and rover have their owncontroller, the receiver and controller can be exclusively mated and noswitching has to take place.

    Magellan Z-MaxThe Z-max is the oldest system in this test;the one we tested was produced in 2003. Thesystem is quite bulky and heavy when com-pared to the other systems and although theweight distribution is good, working with it fora full day becomes tiring. The base and roverreceiver are identical although the UHF anten-na set-up is different. In our test the base hada separate UHF radio module with its ownpower supply. The Magellan is also the only base in the test for whichsettings can be made without the use of the controller; all basic settingsare accessible using the keypad and LED display on the receiver.The UHF antenna used on the rover is mounted between the receiverand the geodetic antenna using a bayonet/screw type mounting. Thereceiver has two detachable units. One of the two is the long-life batterywhich gives an endurance of over 14 hours. The other unit of the testedsystem was an optional built-in GSM/GPRS unit. With the receiver/con-troller combination we tested, the Bluetooth connection constantly lostits connection, requiring a switch to a cable-controlled receiver.

    Sokkia GSR2700 ISXThis was the only receiver in the test that hasnon-swappable batteries although theendurance of the batteries in the receiver islong enough for a single survey day. Due tothe large capacity batteries the receiver is relatively heavy at 1.8 kilograms, making itslightly harder to steady.Due to the fact that at the time of the reviewSokkia did not have two identical systemsavailable, the base tested had a separate radio transmitter that was connected to the receiver using a serial cable. The rover was equipped

    with an internal UHF radio that uses a very small receiving antenna onthe underside of the receiver. Although this set-up makes the receiververy compact without any shielding of the GPS horizon, it is a less optimal configuration for receiving UHF correction signals.The receiver was the only one to have two Bluetooth connections,enabling the user to connect to both an external GSM/GPRS unit andthe controller. The base was also equipped with an optional built-inGSM/GPRS unit.

    Topcon GR-3The GR-3 is the top model of the Topconrange, which shows in a number of cleverdetails. The batteries, for example, can be hotswapped while the receiver is running. Thebattery charger, together with two batteries,can be used as an additional power pack forthe receiver. Finally, standard AA alkaline penlight batteries can be used in a batterycasing that holds four penlights. The receiver and base are identical and can be swapped without a problem. The receiver feels very robust and heavy, which it is at 1.9 kilograms. Due to the weight, steadying it can become tiring after a fullsurvey day. On the other hand, the receiver is built so sturdily that Topconguaranties it can withstand a fall of two meters. The GR-3 was the only receiver with reception for all current GNSS systems including Galileo. Although theoretically an advantage, there iscurrently only one Galileo (test) satellite, and few satellites transmittingsignals other than the regular L1 and L2. When this changes in the yearsto come, the GR-3 will be ready and will not require a hardware update.

    Trimble R6 GNSSThe R6 GNSS receiver we tested from Trimbleis not very different from their top-of-the-rangemodel, the R8 GNSS. The main difference lieswith the reception of the L2C and L5 GPS frequencies. Since there are few satellitesbroadcasting these signals at the moment, thedisadvantage in everyday use is small.Apart from the frequencies, the model is similar to the R8 and is very compact. Thebase and rover are identical, making it easy to swap them. The UHFantenna is located on the underside of the receiver; it therefore doesnot shield the GPS horizon. The downside of this location is that theUHF reception is degraded, which is especially noticeable at longer distances.The receiver is relatively light at 1.3 kilograms. The downside is that thebattery used is very small and has the shortest endurance of the systems in this test. The base will therefore usually be equipped withan optional power pack (not tested).The supplied controller, the TSC2, is relatively heavy but feels very robust.The touch screen is very bright and easily readable. It has three cardslots and can, as with the Topcon controller, directly connect to a USBmemory stick.

    Prod_GEO_6_2007:Prod GEO66 24-08-2007 14:00 Pagina 17

  • Weight TestsIn the world of land surveys, where GPS isconsidered size does matter, not so much inmachine control or for the base station butmostly for the rover. Land surveyors have tocarry the equipment around for hours on endand hold it as steady at the end of the dayas they did at the beginning. Of course it is not just the total rover weightthat is important, but its distribution aroundthe pole as well. The less weight on top ofthe pole the better, since this makes steady-ing the pole easier. A light controller alsohelps, while the weight of the pole has onlya limited effect on overall weight distribution.As well, the receiver/controller combinationhas to be well balanced.Finally, the smaller and lighter the overall set,the easier it is to install in remote locations.I weighed the various system componentsusing a kitchen scale accurate to within 10grams and, for those components such as thetripod and the filled cases that were too heavyfor the kitchen scale, a body weight scale witha resolution of 500 grams.The weights given are the weights with a single set of receiver batteries as supplied bythe manufacturer. Since some manufacturersuse smaller batteries than others, this willaffect the weight of the receiver, but also themaximum endurance.

    Rover WeightThe average pole weight was 4.2 kilograms.The Leica receiver was, at 1.2 kilograms, thelightest in this test (although the Magellanwith the separate antenna/receiver set-up hadthe least weight on top of the pole). However,due to its rather large controller, radio andbracket, the total pole weight of the Leicaexceeded that of the overall lightest rover in

    Base WeightMost brochures only state the rover weight,giving the impression that the base and over-all weights and sizes are not important. Thecomplete system has to be transported to thesite, however, with the last few hundredmeters usually by hand. We therefore alsomeasured the weight and size of the othercomponents. The total weight of the base was calculatedfrom the measurements, based upon the useof a standard tripod weighing 7 kilograms.Again the Trimble came out lightest at only9.5 kilograms and the Magellan and Leica theheaviest at 11.5 kilograms. The weight of theMagellan does not include the mandatory 13.5kilogram battery needed to supply power tothe separate UHF radio transmitter.

    Overall Weight and SizeThe total weight and size of the cases wascalculated as well. Have you ever wonderedwhy GPS representatives drives such big cars?It is not so much the result of the profits theymake, but more the immense size of the sys-tems. Excluding the tripod, pole and looseaccessories, the storage volume of the casesfor a single system varied between 45 litres(Trimble) and 92 litres (Magellan). The totalvolume of all the cases for the systems test-ed was 354 litres which, together with thepoles and tripods, is enough to fill the backof a medium-sized European station wagonwith the back seats folded down.The weight of a single case was always lessthan the Dutch legal limit for workmen, 25kilograms, with the two Leica and Sokkiacases the lightest at 8 kilograms apiece andthe single Topcon case the heaviest at 15 kilo-grams. Of course the total volume and weight

    our test (Trimble, 3.6 kilograms) by 300grams. The heaviest receiver in this test was theMagellan with a total pole weight of 5.7 kilograms. On the plus side, the Magellan canalso be used as a backpack receiver, reduc-ing the pole weight by an estimated 1.5 kilograms. Moreover, most weight in theMagellan is halfway down the pole, makingit relatively easy to steady the pole. In general the heavier rovers ran longer onone set of batteries, a full survey day ormore, than the lighter models in this test.The best weight/endurance results were achievedwith the Topcon and the Sokkia which bothhad a total on-pole weight under 4 kilograms,and which lasted over 10 hours on a singleset of batteries.

    September 2007Latest News? Visit www.geoinformatics.com 19

    Review

    RTK GPS systems are high-volume products.

    Antenna layout on the roof of the car for the range test.

    Prod_GEO_6_2007:Prod GEO66 24-08-2007 14:00 Pagina 19

  • of the cases depends on the type of case andthe options selected by the client. All repre-sentatives, however, claimed that the casesand options supplied were those usuallyselected by their clients.

    Range Test Set-upFor this test we wanted to see what the max-imum achievable range was for the systems.This is especially important when using thesystem over larger survey areas. All manufac-turers were requested to supply a system setto a legal frequency and power setting. Imeant 439 MHz and 500 mW but did notcommunicate this explicitly at an early stage.As a result some systems were set at otherpower settings, with the Leica for examplebeing set to 1 W. At the time I thought thiswas illegal but Leica corrected me, referringme to the website of the Dutch Telecom agen-cy. The difference in power settings, however,meant that comparing the results would behard. We did proceed with the range tests,though.In order to test the ranges under comparablecircumstances a specific set-up was needed.Therefore all five bases were erected fivemeters apart in a row at a straight angle tothe range, a road on an unobstructed dike.During this test both the Sokkia and theMagellan were at a slight disadvantage sincetheir base antennas had to be mounted onthe legs of the tripod, resulting in a slightlylower antenna height which can, potentially,

    reduce the maximum range.The five rovers were then mounted one meterapart on the roof of my car in such a way thatalmost all antennas (both GPS and telemetry)had a free field of view. The exception wasthe UHF antenna of the Magellan which, dueto its construction, had to be mounted slight-ly lower than the others to prevent it fromshielding other GPS antennas, giving the sys-tem a slight disadvantage (see photo).The systems were than set to continuousposition logging with the exception of theSokkia, which did not have this option in thesupplied software. The Sokkia was thereforeread manually. With the systems thus set, thecar was driven along the dike at speeds neverexceeding 10 m/s. At the end of the dike, thecar was turned around and the test wasrepeated in the other direction.

    Range ResultsThe results varied greatly and proved hard tocompare. On average the range varied fromslightly over 2 kilometers to over 7 kilome-ters. Some systems, however, had troublemaintaining lock during this test, without anyobvious reason at the time. One of the problems with a test like this is

    September 200720

    Review

    Performing the initialization test with a piece of tinfoil.

    Prod_GEO_6_2007:Prod GEO66 24-08-2007 14:01 Pagina 20

  • User Interface

    Leica GX1230 GGThe software on the Leica controller has quitea few options. A first-time user can easily getlost in all the menus and settings. The advan-tage of all these options, of course, is that thesystem can be specifically geared towards aspecific application. The controller is also theonly one that can be fully and easily controlledusing the keyboard. The rover was suppliedwith the new colour touch screen that is veryeasy to read, even in bright sunlight. I personally felt that the touch screendid not respond as well to the pen as the greyscale screen on the basecontroller. Logging data is relatively simple once the unit has been setup. Data can be logged to a CompactFlash card slot in the receiver.Exporting data is simple once the export format has been defined usingthe office software. No standard export formats are provided with thecontroller, although the office software holds a number of formal templates that can be used as is or modified.Leica also provides a controller simulator, making it possible to changesettings and to export towards specific formats without having to havethe physical controller in the office. The operation of the simulator isidentical to the controller and can even be configured to display in eithergreyscale or colour.

    Magellan Z-MaxThe Z-max is the only receiver in this test thatdoes not have Glonass support. Furthermore,due to the fact that I seem to have had SBASswitched on during the tests, the Magellanstructurally received two to three fewer satel-lites than the other systems. This is a result oftwo channels being dedicated to receivingSBAS corrections, which means fewer channelsavailable for satellite tracking. The result is thatit was harder for the receiver to get an RTK fix in the re-initialization tests.The software used with the Allegro controller was the commercially available Fast Survey package. This package is very easy to understandand use and has all the features one needs in the field. Data export ismainly towards standard ASCII text files, which can be read by most processing software. If needed, export to shape and dxf formats is alsoavailable. Due to the limitations on the controller, data export has to beperformed using ActiveSync over a serial cable, which can be a problemsince fewer and fewer computers are equipped with a serial port. A serialto USB converter or the optional USB dock can be a solution, but someconverters will work better than others.

    Sokkia GSR2700 ISXConfiguring the Sokkia system is relatively easy.The base requires no settings at all: simply switch it on and it will start measuringand transmitting results. All settings can bedone in the controller from the rover location,where the base position as transmitted fromthe base can be overridden. Sokkia has the only talking receiver. Althoughother manufacturers have a talking controller,none has a receiver that can quite clearly (and in different languages!) tell

    you that you just lost RTK. It is somewhat of a gadget, but it enablesoperation without having to look at the controller all the time.The Allegro controller ran Sokkias own software. The software performsall basic tasks, but has no options for auto logging or extensive attributeinformation. For this reason no points are displayed in the precision testresults.An advantage of the software is that it stores its information in a relational database. This makes adjustment of the results possible on thecontroller without having to use any office software. Just change the basecoordinates, and all points measured from that base will shift with it.

    Topcon GR-3As with most manufacturers, Topcon uses asingle software package for all its land surveyinstruments. The package has a very simplelayout and surveying is relatively easy. I personally find inputting values into the software a bit of a nuisance since only anonscreen keyboard is available with the supplied controller (FC200). The layout of thisonscreen keyboard is not QWERTY, which takessome getting used to.Communication between controller and base/rover is usually done usingBluetooth. With this particular setup the controller lost the Bluetoothconnection every now and then, even with the controller close to the rover.Exchanging data with the office computer can be via data card, USB connection or with a USB memory stick. However the USB port only takesvery slim memory sticks such as the one supplied by Topcon Europe.The ports are very well shielded from dust and moisture by rubber flapsthat open and close without a problem.After a full day of testing and one day in storage the battery of the controller was empty and had to be replaced. It seems the controlleruses power even when shut off.

    Trimble R6 GNSSWhenever the radio signal was lost during thetests, a computer-generated female voice provided you with information. Similar to theSokkia, this is something of a gadget, but itmakes it easier to detect problems with multiple systems running or when temporarilyperforming other duties.The Trimble and Leica receivers were the onlyreceivers that give only global status informa-tion on the receiver itself, requiring the controller to be connected to thesystem for more exact information. Both also display the informationfrom the base in the controller display of the rover.Exporting both the position information and the quality information in asimple ASCII file proved impossible with the installed export formats.Additional formats can be easily downloaded from the Trimble website,however, giving a broad range of export possibilities.

    September 2007Latest News? Visit www.geoinformatics.com 21

    Review

    Prod_GEO_6_2007:Prod GEO66 24-08-2007 14:02 Pagina 21

  • in 1.5 meters of each other, with all the basesin the same configuration as for the range test.The average distance between bases and roverswas in the order of 25 meters.With this set-up, each receiver GPS antenna wasin turn shielded using tinfoil. As soon as therover reported a loss of RTK and the numberof satellites in view remained at a steady lowvalue, the foil was removed. The time betweenremoving the foil and the moment the roverreported an RTK fix was taken as the initializa-tion time. The test was performed three timesper rover within a short time span (minutes).

    Reacquisition ResultsAlmost all systems re-initialized within, on aver-age, 15 seconds, with the Sokkia slightly fasterat 10 seconds. Only the results for the Magellanwere higher, but not comparable due to anincorrect setting in the receiver. It seems that Ihad the SBAS option turned on during thetests, which reduces the number of availablechannels for GPS measurements by two.Considering that this reduces the number ofsatellites available for the solution, initializa-tion times increased. I estimate that, on thisshort baseline, the results would otherwisehave been comparable. One can, however, question the effect of thesedifferences in survey practice; all the systemsinitialized before the average surveyor wouldhave reached the next survey point and stead-ied the pole.

    Endurance Test Set-upThe field endurance of an RTK UHF system ismainly defined by the endurance of the baseand therefore by the batteries used in the

    September 200722

    that there are five transmitters operating atsimilar frequencies, albeit not exactly thesame. Frequencies close to each other cancause crosstalk, making it harder for thereceiver to maintain lock. Further, since the frequency used is line ofsight, every obstruction between the base androver will deteriorate the range. This can bepartially solved by elevating the base anten-na. The range selected was, however, free ofobstacles for 7.5 kilometers, apart from theoccasional passing car. Since the results varied and had some unex-plained gaps in them where receivers lostlock, I investigated the measuring conditionswhen manufacturers reported that the rangesmeasured were not representative. When Ichecked the ionospheric conditions during therange test on the morning of July 11, I foundthat they were truly bad, which probably wasthe reason some receivers were losing lock.Due to this the actual results of the range testare not shown here since they are not repre-sentative of the range under more normalconditions. One thing I did notice, though, isthat having the antenna on top of the GPSantenna certainly provides an advantage.

    Reacquisition Test Set-upThe reacquisition of the RTK fixed solution afterpassing under a tree or bridge is importantsince every second spent waiting seems to beone too many in the field. The actual reacquisi-tion time depends on various factors amongwhich are the numbers of satellites in view, theirconstellation, and the distance between baseand rover. In order to test the reacquisition timeas reliably as possible, all rovers were set with-

    Ionospheric conditions (Kp index) during range test (source: www.sec.noaa.gov)

    Prod_GEO_6_2007:Prod GEO66 24-08-2007 14:02 Pagina 22

  • base. Although all manufacturers can supplyadditional power packs, in this test only thesingle set of internal batteries delivered withthe system was used. The endurance test wasrun parallel to the other tests, with the timesof switching on and off being noted. Usingthe auto logging function, the time of shut-down was determined to within the closesthalf hour.

    even a 12-hour survey day. The endurance ofthe Magellan is largely the result of the sepa-rate battery used for the UHF radio and thelarge 8.8 Ah internal batteries.Almost all rovers ran longer than their corre-sponding base systems. The exception wasthe Leica, where the base ran 1 hour longerthan the rover. This is the result of a differentset-up for the base system, with the base hav-ing larger batteries.Almost all controllers had a battery that last-ed longer than the rover they were coupledto. The Topcon controller only lasted through-out the first survey day. It seems however thatthe controller does not completely switch offand uses power even in off mode. The bat-tery on the Magellan controller came close torunning out, but considering the uptime ofthe Magellan rover this was no surprise.

    Precision TestAn RTK system is bought for its accuracy ofcentimeters or better. Without a proper laboratory set-up it is not possible, however,to test both the precision (standard deviation)and reliability for all the systems under exactly the same conditions. Instead we onlyperformed a quick field test to check precision. During this test we left all systems

    Battery results always depend onthe conditions under which they areused: the colder it is, the less per-formance one gets. During thesetests the ambient temperature wasbetween 18C and 22C.All batteries were charged using thesupplied battery chargers until theindicator showed the battery was inthe green or no longer charging. Thesystems were then run until theyswitched themselves off, a conditionthat is not optimal for the systemand should be avoided in everydaypractice.

    Endurance ResultsSurprisingly, in their brochuresalmost all manufacturers are pes-simistic when they state the

    endurance of the system. On average the sys-tems ran 1.5 hours longer than stated, theexception being the Topcon, which ran 2.5hours less than stated in the brochure.The first base to stop function was theTrimble; it ran for 5.5 hours not nearlyenough for a full survey day. The longest torun was the Magellan with a base enduranceof around 14.5 hours: more than enough for

    September 2007Latest News? Visit www.geoinformatics.com

    Review

    Results of the precision test (Green = Leica; Red = Magellan; Blue =Topcon; Yellow = Trimble)

    Test results. Notes:M = measurement based upon system tested (see text for details)G = as given by manufacturer( ): Optional; see additional remarks1: Including mounting bracket and radio receiver where applicable2: With the pole/pole mount delivered with the system3: Excluding optional power packs and including tripod and bracket as delivered.4: Approximate size/weight of the filled cases delivered with the system, excluding

    tripod and pole

    5: Maximum initialization time measured during tests/given by manufacturer6: With a single set of standard batteries required to operate the system7: The controller ran out after the first 6 hours8: Model reviewed included GSM/GPRS 9: Model reviewed included UHF10: Excluding 13.5 kilogram required base battery11: Results were not comparable due to an incorrect setting in the receiver

    Leica GeosystemsGX1230 GG

    MagellanZ-Max

    SokkiaGSX2700 ISX

    TopconGR-3

    TrimbleR6 GNSS

    23

    Prod_GEO_6_2007:Prod GEO66 24-08-2007 14:28 Pagina 23

  • Manufacturers Remarks on the Results

    Leica GX1230 GGThe range performance of Leica might be tempered by the test set-upbut not by ionospheric conditions. The antenna position, radio equip-ment quality and line of sight are important aspects to guarantee receiv-ing of corrections signals. On the reacquisition and precision test results,just a fast TTFF is ignoring the reliability. The Leica precision test showsthe best repeatability with small position spread. No outliers supportthe fact of reliability. GPS1200 realizes this by solving the ambiguitiestwice and independently before providing a fix.

    Magellan Z-MaxThe Magellan Z-Max is a truly ultra-flexible survey system that lets sur-veyors control their survey their own way. It permits surveyors to selectonly the modules they want for the most cost-effective survey solution. TheZ-Max is available to survey in NTRIP, VRS, or FKP networks; GPRS oreven UHF+GSM/GPRS. It switches seamlessly from post-processing toRTK, and it is suitable as either a base or rover. The detachable modulesmake configuration changes and system upgrades simple. And, if yourelooking for a high-precision RTK solution at about half the cost of any ofthe systems tested in this article, take a good look at the new MagellanProMark3 RTK with BLADE, the new Magellan GNSS engine.

    Sokkia GSR2700 ISXThe Sokkia GSR2700 ISX is proofed as a user-friendly receiver with excel-lent environmental specs and a strong RTK performance. We would havewelcomed a test of long-range RTK performance since the GSR2700 ISXexcels in quick and reliable RTK solutions over long distances, which canbe related to the reacquisition results. Furthermore Sokkias controller soft-ware SDR+ is positively received where its strong feature is freedom in thefield. Thats why we built SDR+ based on a relational database environ-ment. Sokkia is determined to serve surveying professionals with reliableand accurate positioning solutions such as the GSR2700 ISX, now and inthe years to come.

    Topcon GR-3This field review is a good practical test. It proves that Topcon's GR-3 isa leading product and performs well when compared to others. Its uniquedesign helped achieve the longest range at only 0.5watt radio power.Although the GR-3 is claimed to be heavier than some, it should beremembered the battery life is sufficient for a full day, so no extras areneeded and it includes a built-in GSM/GPRS, which others have to add.The fact that the GR-3 is ready for Galileo means no costly hardwarechanges or add-ons are needed as the satellite program progressesbeyond the current single satellite, making the unit future proof. As thetest proves, the GR-3 is ready for all aspects of current and future use.

    Trimble R6 GNSSThe Galileo satellite radio navigation system proposed by the EuropeanUnion offers advantages to Global Navigation Satellite System (GNSS)users by providing additional satellites, additional signals, and compati-bility with GPS. Trimble fully supports this advancement in the GNSSmarket. As we have done with products that capitalize on next-generation GPScapabilities, we are committed to having Galileo-compatible productsavailable for our customers well in advance of Galileo system availability.In the case of GPS Modernization, our compatible products were avail-able a year ahead of the first L2C-capable satellite launch. Trimble hasalso developed products for the coming L5 GPS signal. Likewise, we will offer equipment with Galileo capability well ahead ofthe time when production satellites are launched. In the meantime, it isour goal to offer the most productive and competitive equipment thataddresses our customers' needs both now and in the future.

    You can also find a movie of the test in our movies sectionon the website www.geoinformatics.com.

    September 200724

    Review

    running after the initialization tests.The data was logged for roughly one hour at30-second intervals for all systems with theexception of the Sokkia whose software didnot support auto logging. The resulting position plot for each system was then shifted towards an imaginary central pointusing software in order to be able to comparethe results visually.

    Precision ResultsAlthough the test as performed by us is nota true indication of the precision of the systems, it gives a good idea of the differences between the systems and therespective settings made within the software.For example, with the incorrect SBAS=ONsetting the Magellan lost RTK lock at somepoint during the tests and therefore loggedfewer points, which in turn were very close

    together. The Topcon on the other hand hadno problem getting into RTK lock but seemsto have had some multi-path problems during the test resulting in a larger positionspread. The standard deviation for all systems, whenlocked, was well within the 0.025-meterrange and therefore within expectations forsuch a system. The test did, however, showthat specific settings and differences in software can influence the results.

    ConclusionI tested five systems that are marketed by their respective manufacturers as compa-rable. During the tests we found differencesbetween the systems, not so much in theiruser friendliness or the applications theycould be used for, but in the hardware itself.What is clearly visible from the results,

    though, is that every manufacturer has tomake certain choices in the design phase ofthe system. Some will opt for batteries withlong endurance and accept a higher weightand others value versatility over a simpleuser interface.As such, selection of a specific systemshould be based not so much on the typeof application the software supports butmore on factors such as price, maximum operational range, endurance and weight of the system for the specific application(s)one has in mind.

    Huibert-Jan Lekkerkerk

    ([email protected]) is Editor-in-chief

    of Geoinformatics. For more information on these

    receivers: www.leica-geosystems.com;

    www.pro.MagellanGPS.com; www.sokkia.com;

    www.topcon.eu; www.trimble.com.

    Prod_GEO_6_2007:Prod GEO66 24-08-2007 15:37 Pagina 24

  • Image Quality Is Critical

    Leading the Way to Accurately Visuali

    Ordnance Survey have been providing accurate, reliable and detailed geographic information for more than 200 years.

    As Great Britain's national mapping agency, it provides the most accurate and up-to-date geographic data from complex

    digital information to traditional walking maps for Great Britain, relied on by government, business and the public.

    Although overall performance of their HP Designjet 5500 printer was satisfactory, when HP introduced the HP

    Designjet Z6100 printer, Ordnance Survey was eager to assess its impact on their map printing business.

    By Job van Haaften

    Ordnance Survey offer a complete mappingprocess from flying over the country taking aeri-al photography, to shipping of the final, print-ed products through Ordnance Survey PrintServices. Its modern and extensive in-plant facil-ity at its headquarters in Southampton (U.K.),allows Ordnance Survey Print Services to pro-vide its clients with a one-source total solution.

    Making Deadlines EasyIts HP Designjet 5500 printer played a criticalrole at Print Services, producing large-formatproofs for production printing of maps on off-set machines, and it was used to print the mapcovers themselves on cardboard, printed 8 upon a carrier, showing a picture of the area cov-ered by the map, and with a surrounding silverspot colour. The HP Designjet 5500 printer wasalso extensively used for advertising material,from small A2 posters up to billboard, large walldisplays for trade shows and for shorter printruns on resistant media for specific products,

    such as maps used in the field.Maps and aerial photographs printed on theHP Designjet Z6100 are perfect on the first print.Colours are really vivid and with greater depth,so subtle shading really stands out. Blacks aredense and lines sharp and crisp, creating pro-fessional-quality maps that are increasing ourcustomer satisfaction.Garry Heaton, Prepress Technical BusinessOfficer, Ordnance Survey. Gary describes howthe new printer was an instant success. Themost obvious improvement using the newDesignjet Z6100 printer is the speed of themachine. Its much faster than the Designjet5500, and the quality is much better. The fastprinting takes the sweat off coming up to dead-lines for trade-show displays and other publici-ty material production.

    Clarity and PrecisionImage quality is the critical area for map print-ing businesses. Printed images present an

    series of unique challenges, demanding range,clarity and precision for data-intensive mappingapplications combined with photographic qual-ity for aerial photographs, crisp line drawingsand smooth area fills with subtle tones that canmake all the difference. Garry was delightedwith the results from the new printer. The out-standing print quality from the Designjet Z6100is a selling point for the map. There are peopleout there that buy maps because they just lovemaps. When the maps look that much better,our customers are that much happier. The dif-ference is marked Gary adds. We have a seriesof touring maps where we highlight areas ofBritain that are of a great interest to tourists.We put hill shadings on these, but on theDesignjet 5500 the shading didnt stand outvery well. On the Designjet Z6100 weve noticeda marked difference. Shading is much clearerand crisper. The image quality has improvedimmensely.Thanks to HP Vivera pigment inks, with the HP

    September 200726

    Art ic le

    Ordnance Survey emphasises the big image qualityimprovement of Designjet Z6100 versus theDesignjet 5500 in map printing business when youneed to combine clarity and precision of dataintensive applications with photo quality for aerialphotos. Hotel Metropole in Leeds, 1992.

    Prod_GEO_6_2007:Prod GEO66 24-08-2007 15:18 Pagina 26

  • Three-black ink set (matte black, photo black,and light gray), the HP Designjet Z6100 achievesmillions of colour combinations across a widecolour gamut and across a wide range of media,producing a range of blacks and gray withsmooth, subtle transitions, true gray neutrality,and rich black density. Gary claims the imagequality compared to the old printer has greatlyimproved. For a trade show we laid lots of dis-play images out on a black background, andon the Designjet Z6100 we got much moredepth of colour, a denser black, and much morevivid colours than on the Designjet 5500.

    Printed to Last in the FieldThe HP Vivera pigment inks deliver a combina-tion of outstanding photo-image quality, waterresistance, and fade resistance for over 200

    er. Every map is folded and contained in anindividual cardboard cover with a picture of thearea concerned surrounded by a spot colour,silver. The Designjet Z6100 gives us the out-standing image quality we are looking for, withaccurate colours straight off. HP DreamColor Technologies featured in the HPDesignjet Z6100 printer series, including auto-matic generation of custom ICC colour profiles,Pantone emulation and the embedded spec-trophotometer***, ensure consistent colouracross different printers or presses and a widevariety of media. HP's Closed-loop colour cali-bration accounts for changing environmentalconditions and media adjustments for the lifeof the product. Printing businesses can confi-dently split print runs between two or moreprinters and get consistent colours from themall, even in changing environment conditions,and from print to print at different times. HPDreamColor Technologies are designed tostreamline workflow through integrated, auto-mated systems speeding turnaround timeand lowering production costs.

    Maximizing Use of ResourcesSaving time, maximizing efficiency and minimiz-ing waste are recurring themes for OrdnanceSurvey Print Services, and according to GaryHeaton the HP Designjet Z6100 printer opti-mizes productivity and resource utilization inevery area. Our Designjet Z6100 is going allday, every day. We havent had to change a car-tridge yet. Theyre much larger and the inkusage is a lot more efficient than on theDesignjet 5500. The large-capacity ink car-tridges combined with long HP rolls, giveOrdnance Survey added confidence in trouble-free overnight printing runs.We were printing old mapping, 150 or 200years old, originally hand drawn, covering the

    years.** The HP DesignjetZ6100 printer inks also drymuch quicker than on theold printer. The improvedresistance and shorter dry-ing times also help avoiddamaging prints from han-dling and accelerate finish-ing processes. In combina-tion with the new HPVivera pigment ink durabil-ity, Gary says this is amajor time-saver andallows them to producemaps that can be used inthe field. Prints on plas-tic-like material from theDesignjet 5500 would takequite a while to dry. On theDesignjet Z6100, its a lotquicker. He adds,Changing from dye-basedinks to UV inks on the

    Designjet 5500 was a bit time consuming, butwith the Designjet Z6100 a job comes in for dis-play purposes and theres no problem. With justone ink set for everything all prints are long-lasting so we just go straight ahead and printthe job. Gary is also extremely satisfied that colour accu-racy and consistency are no longer a trial anderror process with the HP Designjet Z6100 print-er, saving time and eliminating waste. Usingthe Designjet 5500, we had to alter colour pro-files a number of times before we got a printthat was not oversaturated in the dark areaswe were wasting time and material there. Onthe new Designjet Z6100 the ink density andcolours are fantastic first time off. Its perfectfrom the word go. Their confidence in the reli-ability and colour accuracy has never been high-

    September 2007Latest News? Visit www.geoinformatics.com27

    Art ic le

    li ze the World

    ChallengesLong Ink-drying times Need faster printing speedsTime consuming changes:Ink-cartridges, media,between UV and dye-based inksHill shades not standing outNeed more vivid colours and deeper blacksNeed sharper line qualityAltering profiles to get the right ink-coverageNeeded better overall image quality and easiercolour management

    SolutionHP Designjet Z6100 printerHP Vivera pigment inks(8 colours)HP media:HP Coated PaperHP Heavyweight CoatedHP Productivity Photo GlossHP High-Gloss Photo Paper

    ResultsProfessional-quality maps that increase cus-tomer satisfactionCustomers happier with faster turnaround More confidence on tight product schedulesQuicker, simpler workflowTime and materials saved Experimentation with different media for newproducts

    Hotel Metropole in Leeds, 2006.

    Prod_GEO_6_2007:Prod GEO66 24-08-2007 15:18 Pagina 27

  • The HP Designjet Z6100 printer deliversmore than 1,000 ft2 per hour (100 m2)*.Eight HP 91 Printheads, provide a widerprint swath, up to 1.8 inches, and thefirst-ever Optical Media Advance Sensor(OMAS) improves paper advance accu-racy, so the printer can print at higherspeeds and regardless of environmen-tal conditions without impeding imagequality.

    Job van Haaften

    ([email protected])

    is editor of GeoInformatics. With special

    thanks to Augustin Comadran from HP. For

    more information: www.hp.com.

    September 200728

    Three different data sets of an area of Southend in the UK.

    country. The Designjet Z6100 had a long roll ofpaper loaded, so we left it to print overnight.The maps looked stunning when we came inthe morning.The outstanding quality and range of mediadesigned with the HP Vivera pigment inks, giveOrdnance Survey greater peace of mind toexplore innovative GIS printing applications.The Designjet Z6100 has opened up the pos-sibility for us to experiment with different mate-rial while always getting accurate colours. Weproduced a series of 40 aerial photographs onphoto paper along with corresponding drawnmaps on transparent paper. The drawings satover the photos to highlight changes on theground. Our customers were very pleased. Itwas probably the first time theyd had some-thing like that done, confirms Gary. OrdnanceSurvey appreciate the flexibility they get fromthe choice of original HP media substrates fora broad set of applications.

    Truly TransformedThe HP Designjet Z6100 printer has truly trans-formed GIS printing capabilities at OrdnanceSurvey Print Services, allowing them to workmore effectively with increased confidence,improving their productivity and streamliningtheir workflow. Gary concludes, Job turnaroundwith the Designjet Z6100 is much faster com-pared to our previous printer, giving us moreconfidence on tight product schedules. Ourworkflow is now quicker and simpler, and thereis no trial and error. The printer efficiency isimpressive, saving us time and materials.

    * On plain paper in Fast mode** Display permanence rating forinte rior displays/away from directsunlight by HP Image PermanenceLab, and by Wilhelm ImagingResearch, Inc. on a range of HPmedia. Water resistance and interiorin-window display ratings by HPImage Permanence Lab on a range ofHP media. For details:www.hp.com/go/supplies/printperma-nence.*** With i1 colour technology.

    Prod_GEO_6_2007:Prod GEO66 24-08-2007 15:18 Pagina 28

  • John Trinder, Emeritus Professor

    University of NSW, Sydney Australia

    1st Vice President ISPRS

    When Will On-Board Processingof Orthophotos be CommerciallyAvailable?

    While digital image processing for photogrammetry has existed for more than 15

    years, it took another 10 years before the first digital aerial cameras became

    operational. However, two solutions for the production of operational digital aerial

    cameras, based either on multiple linear arrays, or multiple area arrays, are now

    available and the market for these cameras is growing.

    The advantages of these cameras includebut are not limited to: Elimination of degrading effects of film

    and improved dynamic range. More data acquisition per day and

    throughout the year, especially in higherlatitudes: for example Aerodata in Belgiumhave reported that during only three daysof perfect weather conditions more than5000 images were taken while KKC(Japan) collected more than 12,000 imagesin 40 projects in a period of 6 months;and in USA, orthophotos were producedof over 1 million square km for the USDAFarm Service Agency in a 3 month period.

    High levels of redundancy leading to aparadigm shift in operations in pho-togrammetry.

    High geometric accuracies. Near real orthophotos with little or no

    need to correct images for relief displace-ment.

    The highest resolution multi-spectralimages for remote sensing applications.

    There has been an explosion in the numberof images acquired by amateur photogra-phers using consumer grade cameras. Thedevelopers of the first digital cameras atEastman Kodak, even in the 1970s foresawthat the applications of digital imagingwould be almost limitless. Likewise, asexemplified by the developments byPictometry International Corp. in USA, andtheir recent expansion by joint ventures intoEurope and Australia and New Zealand, moreaerial imaging, both vertically viewing andobliques, are being acquired than everbefore. This is apart from advances in satel-lite sensing, which also reveal rapidadvances in the acquisition of high resolu-tion images from space.The digital aerial systems are continually

    improving, with new generations of cameraheads with more pixels of smaller sizes, andmore efficient data handling. So far the out-put from digital systems has usually beendigital orthophotos. Line mapping stillrequires manual extraction of features fromdigital images. Photogrammetric softwarecompanies have concentrated on more effi-cient handling and processing of multipleimage types, rather than developing higherlevel information extraction. A great deal ofdevelopment is still required before efficienthigh level systems are available for featureextraction suitable for digital line mappingor GIS databases.

    In parallel with these developments in imag-ing are continued advances in airborne laserscanning or LiDAR systems, with improvedpower, higher frequencies and recently, mul-tiple sensing in flight, which enables morethan 1 pulse to be emitted and received dur-ing a cycle of sending and receipt of a pulse.These latest developments can result inimprovements in efficiency of LiDAR dataacquisition of up to 50%. Processing ofLiDAR data is being significantly advanced,while merging by overlaying of LiDAR andimagery is operational in some digital pho-togrammetry software packages.

    Latest News? Visit www.geoinformatics.com September 2007 29

    The digital aerial systems are

    continually improving, with new

    generations of camera heads with

    more pixels of smaller sizes, and

    more efficient data handling.

    Column

    These advances in both forms of data acqui-sition of the terrain surface have significantfinancial impacts on photogrammetric com-panies which are required to update theirsystems more rapidly that was required foranalogue systems. Therefore, since theamortization period of digital aerial camerasis typically quoted as about 3 years, highthroughput is required to finance them.

    Developments in airborne sensing areadvancing rapidly. While the high level processing for feature extraction will takemany years to become robust and effective,the next step in the advancement of thesetechnologies is on-board processing of someaspects of imaging and LiDAR data acquisi-tion. It seems that the ultimate extent ofthe advances of these technologies will beon-board processing for the commercial pro-duction of orthophotos, though I would notlike to predict when this will occur.

    Prod_GEO_6_2007:Prod GEO66 24-08-2007 14:03 Pagina 29

  • Cognitively More Ergonomic

    Route Directions that Communicate

    Do you remember a person next to you, or yourself, giving route directions? Although these directions can be highly

    individual, following these directions is typically straight forward. They contain the information relevant for reaching the

    destination, are descriptive, they tell a story of route following, and can easily be memorized. The automatically generated

    directions by in-car navigation systems, location-based services and web based route planners look different.

    They are hard to memorize, and their communication is far from perfect. This article discusses the challenges of improving

    automatically generated route directions, recent progress of research in this area, and a first commercial demonstrator

    for some of these results.

    By Stefan Hansen, Stephan Winter and Alexander Klippel

    In-car navigation systems, location-based ser-vices and web based route planners all do it:calculate a route, and communicate it to humanusers. This article looks closer at the secondaspectthe systems communication to ahuman user. The questions addressed here are:Do they speak the same language? Can theyunderstand each other? And if so, how mucheffort is involved in following the given routedirections? Finally, can we design systems thatcommunicate better, in the sense of being moreintuitive in expressing their directions?As navigation services are about to become astandard feature in our lives, it is worthwhileto look at their history and the directions, thatthis technology is currently heading. Early map-based interfaces for in-car navigation did notsucceed: a car driver studying a screen mapwhile driving was not acceptable. From there itwas a short step to verbal route directions. Thisfeature is now quite common also with webbased route planners, which provide both,maps and route directions. Many mobile loca-tion-based services suffer from small screensizes, and up to now have neither come up withconvincing maps nor with convincing voice-based solutions. This is probably one of thereasons why despite recent high sales growthof portable navigation devices, many user expe-riences are unsatisfactory.Interestingly, newer in-car navigation servicesoutplay each other again with visual interfacessuch as perspective views of maps or of tex-tured 3D representations of cities. This happensin the spite of the long realization of cognitivepsychologists and cartographers that more isnot always better. So, where is the balance?What is best for the user? And how can researchhere support commercial product development?

    September 200730

    Art ic le

    Figure 1 Examples of reducing the amount of instructions: A) A common technique is to combine segments withthe same street name Follow Main Road. B) An extension of example A) is to use highway numbers. This allowscovering larger distances in one instruction. C) To indicate the end of a chunk often landmarks can be used Gostraight until you reach the gas station.

    Figure 2 Examples for integrating landmarks in directions: A) A classic example of landmarks Turn right beforethe church. B) Salient intersection along the route can also function as landmarks Take the 3rd exit at the nextroundabout. C) Multiple similar salient features of the environment can be identified by ordering them Turnright at the 2nd traffic light.

    Figure 3 Right turns at different types of intersections: At a t-intersection (A) a simple Turn right is sufficient.Several options to turn right at an intersection (B) require a more differentiated instruction Take the 1st exit onyour right as well as a roundabout (C) Take the 4th exit at the roundabout.

    Prod_GEO_6_2007:Prod GEO66 24-08-2007 14:03 Pagina 30

  • In this paper we concentrate on how principlesof cognitive ergonomics can be used to designbetter structured route directions. These princi-ples will be applied to verbal route directions,but other modes, e.g. by sketch, could profitas well.

    Automatically Generated The current forms of route directions werederived more from the sort of data availablethan from a user perspective. Street networkdata, available in several levels of detail andrich in attributes, suggested a structure of direc-tions based on sequences of street networksegments. Instead of referring to each singlesegment, simple grammar allows amalgamationof segments between turns, leading to standardturn-by-turn directions. Turn-by-turn directions are tabular directions allof the same grammatical form and level ofdetail. What can vary between different naviga-tion services is the chosen vocabulary and theset of attributes referred to in the directions.There is, however, a common denominator incurrent route directions and that is the streetname and the distance. So, whats wrong with standard route direc-tions? Well, they are not always easy to follow,which means that travelers concentrate lessthan desired on traffic while following the direc-tions:- Humans are not necessarily good in estimat-ing distances. So the only way to exactly fol-low distance-based directions would be to con-stantly keep an eye on the odometer neithera practical nor a desirable condition. Distances

    memorable. In order to generate automaticroute directions with these characteristics, thefollowing three principles should be realized.

    Fewer directionsThe fewer directions that are given to the trav-eler, the easier they are to memorize. In partic-ular simple, obvious instructions can easily bemerged in one single instruction without omit-ting any information required to successfullyfollow the directions. For example Go straightat the next intersection and Turn left at thefollowing intersection can be combined toTurn left at the second intersection. However,a navigation service should offer the user accessto merged directions, for the case, that theyreq