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Digital Aerial Sketchmapping Interim Project Report

Charlie Schrader-Patton Remote Sensing Applications Center

USDA Forest Service 2222 West 2300 South

Salt Lake City, UT 84119

H. Ross Pywell Forest Health Technology EnterpriseTeam

USDA Forest Service Building A, Suite 331 2150 Centre Avenue

Fort Collins, CO 80526-1891

United States Department of Agriculture Forest Service

Remote Sensing Applications Center Salt Lake City, Utah

Forest Health Technology Enterprise Team Fort Collins, Colorado

RSAC-7140 LSP 0001 - RPT 01 February 2000

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EXECUTIVE SUMMARY Due to recent advances in microprocessor speed and PC system performance it is

now possible to use portable computers to aid aerial sketchmapping. The USDA Forest Service, Forest Health Technology Enterprise Team (FHTET) and the Remote Sensing Applications Center (RSAC) have worked with a commercial vendor, GeoResearch, Inc. to develop a product that will meet the needs of forest health aerial surveyors. This system offers the advantage of tracking the aircraft location on a moving map display, eliminating the need for the surveyor to spend extra time locating and mapping forest damage, and resulting in higher quality data. In addition, savings in digitizing time make this new technology attractive because a digital product is created during aerial data acquisition. The current method requires translation of a paper map to a digital file; with the new digital system, features recorded from the aircraft are seamlessly imported into a Geographic Information System (GIS).

ABSTRACT

Aerial sketchmapping is the geo-locating of land features observed from an aerial

platform and the subsequent recording of these features on maps or photographs. This report describes a project to develop a digital aerial sketchmapping system to replace or augment the current system where features are sketched on hardcopy maps or photos. We investigated several hardware and software options. Advantages to the digital system include automatic tracking of the aircraft position on the map base through a link to a Global Positioning System (GPS) receiver and reduction of time spent digitizing data into a GIS. Future enhancements to the system include software modifications to the user interface, developing a dual input system, and expanding the types of data used as background maps. Continued close cooperation with the sketchmapping community is critical to the success of this project.

INTRODUCTION

This report documents our efforts to develop a digital aerial sketchmapping system

for forest health aerial surveyors. A brief history of the project is presented, including the software and hardware investigated. The current system is described and potential future work is discussed.

Aerial sketchmapping for forest health protection has been conducted since the 1940s. Typically, sketchmappers fly over the area being surveyed in a high-winged, high performance monoplane such as a Cessna 206 (Figure 1) at elevations of 1000 to 3000 feet above ground level. The sketchmapper tracks the location of the plane on a hardcopy map or aerial photograph and sketches areas of forest that have been damaged by insects, disease or weather events. The hardcopy products are provided to the Forest technicians for data entry. The sketched features (points, lines, polygons) are heads-up (on-screen) digitized into a GIS, and these data are then used to prepare reports at the Forest, Region, and national levels.

Problems with the current manual system include managing numerous maps in the cockpit, the inaccuracy of sketched features, and the office time required to digitize sketched features.

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Figure 1. High-winged monoplane typical of the type used in aerial sketchmapping.

The accuracy of sketched features is dependent upon the ability of the sketchmapper to track the position of the aircraft on the map, and to correctly relate features seen on the ground to the map. This can be especially difficult in unfamiliar and/or flat terrain. At typical airspeeds of 90 to 120 knots, a sketchmapper has approximately 15 seconds per square mile to accurately locate, sketch and attribute features (assuming a visual mapping distance of 2 miles from the aircraft). Accuracy is a relative term, and the end use of the data must be considered. If the data collected during a sketchmap mission is for general overview monitoring purposes, then more error can be tolerated than if field crews are going to locate affected stands using the sketchmapped data.

After the survey flight, the hardcopy maps are delivered to GIS technicians who must accurately digitize and attribute the features into a GIS. This is costly both in terms of staff and contract time and funds.

Advances in GIS, GPS, and in computer technology led to interest in developing a digital system of data collection that might help solve some of the problems associated with the manual method. It is important to note that even with its inefficiencies and lack of accuracy, the current manual system works. Digital enhancements to this system must result in substantial improvement over the current methods to be justifiable.

BACKGROUND

Interest in the development of a digital aerial sketchmapping application led to a

request in Fiscal Year 1995 by the Pacific Northwest Region to the Forest Health Technology Enterprise Team and the Missoula Technology Development Center (MTDC) to initiate an information-gathering project regarding the feasibility of developing a digital system. As a part of this project, forest units throughout the United States were surveyed to determine the needs of the sketchmapping community. A trip to the British Columbia Forest Service in Williams Lake, B.C., was taken in June 1996 to examine and demo their digital sketchmapping system.

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The system developed by the B.C. Forest Service operates on a laptop PC linked to a GPS receiver and allows the user to sketch on the screen using a standard trackball mouse. The software used in this system was developed by the B.C. Forest Service using Microstation MDL programming language and requires a full installation of Microstation software. Data input and user-interface features include aircraft position displayed on-screen as an icon, background map rotation based on the direction of travel, and attributing of features using pre-programmed function keys. Disadvantages identified were the small size of the screen on the laptop computer, the lack of screen brightness, the awkwardness of the mouse pointing device, and data incompatibilities between Microstation and ESRI Arc/Info. (Arc/Info is the standard GIS software for the USDA Forest Service.) In general, the system was slow and cumbersome.

Two other systems were also reviewed, AvCan Technologies of Pitt Meadows, B.C., and ArNav of Puyallup, Washington. These reviews provided a look at functioning systems and the current state-of-the-art technology. (For a complete discussion of this information-gathering project, see Thistle, et al., 1996.)

A list of requirements for a digital aerial sketchmapping system was developed as a result of this project:

1. The map display must be linked to a GPS receiver so that an icon on the display

represents the current position of the aircraft. 2. The map display must update quickly at ground speeds of 130 mph. 3. The screen must be viewable under a variety of lighting conditions, including

full sunlight, and also display in full (256) color. 4. The viewable screen size must be at least 10.4” measured diagonally. 5. The software must have the capability to:

(a) Digitize points, lines, and polygons (including nested and overlapping polygons)

(b) Attribute digitized features (points, lines, polygons) quickly and easily (c) Edit feature attributes (d) Allow the user to define the feature attributes to be collected (e) Collect the GPS log file of the flight (f) Allow the user to zoom to different map scales (g) Accept common raster and vector data types as background maps (h) Export files in a format that is easily imported into ESRI Arc/Info (i) Save data automatically to the computer disk (j) Update the screen map display based on the GPS position and heading of

the aircraft 6. The hardware should be operational in moderately harsh conditions (32 to 120

degrees Fahrenheit, high humidity, dusty conditions). 7. The primary input device must be a touchscreen with stylus.

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SYSTEM DEVELOPMENT: SOFTWARE

Using these requirements, the Remote Sensing Applications Center began an

extensive search for hardware and software adequate for the task. The initial investigation into software focused on commercial off-the-shelf (COTS) products that came close to meeting our criteria. We focused on the following software:

Aspen Card by Trimble DynaMo-GIS by GeoFocus FieldNotes by PenMetrics, Inc GPS-Pro Map by MPN Components PenMap by Condor Earth Technologies GeoLink PowerMap by GeoResearch

These companies were also asked if they could modify their COTS products to meet our criteria.

Based on this investigation, we selected GeoLink PowerMap by GeoResearch, Inc. of Billings, Montana. GeoResearch agreed to make the necessary modifications to their COTS product to meet our sketchmapping needs. These modifications were done under a GSA special services contract.

When collecting data using PowerMap, the aircraft position is displayed as an icon on the map display along with feature (point, line, polygon) type keys, and a user-defined keypad for attributing features (Figure 2). The observer selects the particular type of feature to be sketched, sketches the feature on the screen, and then attributes the feature using the keypad. The screen remains frozen while the feature is being sketched and updates after the ‘Enter’ key is pressed. When the aircraft icon advances to the edge of the window, the map display updates with the aircraft icon moving to the center of the window.

Upon completion of the sketchmapping mission, a translation step converts the sketched features into ESRI shapefiles. These shapefiles are then copied to a floppy disk for transfer to a GIS.

Sketchmappers can chose from a variety of map bases; typically those in the Rocky Mountain states use 1:100,000 scale, USGS 30- x 60-minute quadrangle maps, while others prefer Thematic Mapper Satellite-based imagery or digital orthophotography. The GeoLink software is able to display many different types of geospatial data as background maps and so is able to accommodate these various preferences.

Using large map files tasks the CPU with reorienting these files in response to changing GPS position. The resulting drain on computer resources (memory, virtual memory) caused screen refresh times to be unacceptably slow. This problem was partially addressed by acquiring computers with lots of added memory, but we sought a more robust software solution. GeoResearch engineers developed a built-in utility that divides large map files into tiles that represent commonly used zoom scales. Instead of rotating and displaying the whole map file, the improved software can display only the map tiles adjacent to the current GPS position. This map tiling utility is currently in beta form, but initial tests are promising.

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Figure 2. Screen display of the GeoLink PowerMap software during data log-ging. The software displays sketched features and rotates and pans back-ground data as the aircraft moves over the terrain.

Figure 3. Computer Dynamics Flat Panel Display Computer

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Figure 4. The GeneSys 133 from Xplore Technologies.

Figure 5. Current hardware configuration for digital sketchmapping.

SYSTEM DEVELOPMENT: HARDWARE

Initially, we tested a touchscreen computer manufactured by Computer Dynamics of

Greenville, South Carolina (Figure 3). Although the screen size and brightness of this computer were adequate, its size, weight, and heat output prohibited its use in a small aircraft.

Next, we tested the GeneSys 133 from Xplore Technologies of Austin, Texas. This computer is attractive because the CPU and touchscreen are housed in a single, compact unit (Figure 4). Preliminary tests were promising, but the touchscreen was not bright enough to be visible in direct sunlight.

The current hardware setup for our systems generally consists of a laptop PC with a

Pentium II 300Mhz processor and 190MB of RAM, an external touchscreen monitor, and a GPS receiver (Figure 5, Figure 13). The system is powered from the aircraft using a specially designed power distribution board that draws from the 28VDC supply on the aircraft. The GPS receiver uses an antenna modified with suction cups to attach to the inside of the aircraft window. The GPS signal enters the PC via serial port connection. We tested many GPS receivers, and it seems that any receiver capable of producing an NMEA 0813 output string will be compatible with the software.

We tested three types of touchscreens that vary in screen size, b r igh tness , and touchsc reen technology.

The first touchscreen tested was manufactured by Cascade T e c h n o l o g y C o r p o r a t i o n o f Farmington Hills, Michigan, and was fitted with an ELO Accutouch resistive touchscreen. The screen is 10.4” measured diagonally, 500 nits in brightness, 800 x 600 in resolution, and weighs 7.5 pounds. Resistive touchscreens have a membrane layer

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Figure 6. The 15” Peavey touchscreen (L) , and the 12.1” KDS touchscreen monitor (R).

installed over a fine wire mesh grid in the screen; when this membrane is pressed onto the grid, a signal is sent to the computer and the cursor jumps to that spot on the screen. Virtually any object can be used on the screen–your finger, an eraser, stylus, etc. This can be problematic when sketchmapping, because an inadvertent touch to the screen may cause undesired actions to be invoked. The 10.4” Cascade screen was also rather small in screen size and limited the amount of map area visible on the screen.

KDS PixelTouch of Ontario, California, manufactured several screens to our specifications (Figure 6). These screens are 800 x 600 in resolution, 12.1” in screen size, 1500 nits in brightness, and have capacitive touchscreens installed. This type of touchscreen is activated by completion of an electrical circuit using a tethered stylus. This technology avoids the inadvertent activation problem of the resistive touchscreen because the screen can only be activated with the tethered pen.

Preston Peavey, Inc. of Marietta, Georgia, has built a 15”, 1024 x 768 resolution, 1000 nit, capacitive touchscreen monitor (Figure 6). Advantages of this monitor include larger screen size and higher resolution. Preston Peavey has also built a special, ruggedized computer with a built-in GPS specifically for use in an aircraft (Figure 7).

Most of the hardware is installed in the cargo area of the aircraft or in the rear passenger seat (Figures 8, 9) for safety reasons. Once the system is up and running,

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Figure 7. PC-104 ruggedized PC computer with Garmin GPS receiver

Figure 8. The system must be carefully installed in the plane to prevent damage to cables and connections during flight.

the sketchmapper operates the software while holding the touchscreen on his/her lap (Figures 10, 11).

The advantages of the laptop-based hardware setup are low cost and flexibility. We established a goal to keep the total system cost under $8,000 (Thistle, et al., 1996). Assuming the sketchmapper already has a suitable laptop PC and GPS receiver, the cost would be approximately $5,900 to $8,100, depending largely upon which touchscreen monitor is preferred (Table 1). This cost estimate does not include the purchase of background map data. The laptop PC can be used for other general computing purposes and can be upgraded as faster processors and more memory become available. This flexibility also applies to the GPS receiver, which can be used for field data collection as well as for sketchmapping.

Since most laptop PCs only have one serial port installed, it is necessary to purchase and install a serial port adapter device. Two serial

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ports are necessary: one for the GPS and one for the touchscreen monitor. We have tested PCMCIA- and USB-based serial port adapter devices, and the USB devices have proven to be easy to install and use. Older laptop PCs may not have USB capability and thus will use the PCMCIA adapter.

The disadvantage to the laptop-based hardware setup is that it is somewhat awkward and cumbersome with many different components and cables in the confined space of a

Figure 9. The laptop PC can be stowed behind in the passenger seat for easy in-flight access.

Figure 9. The sketchmapper operates the software via the touchscreen.

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Item Cost

Cascade Technology SBR104 Touch-screen Monitor

$3,800

KDS PixelTouch Touchscreen Moni-tor

$4,000

Preston Peavey Touchscreen Monitor $6,000

GeoLink PowerMap and Mapping Companion Software

$1,600

Power distribution equipment, Serial

Total $5,900- $8,100

Figure 11. The touchscreen is visible in full sunlight.

Table 1: Estimated costs of digital sketchmapping hardware/software 2000).

small aircraft. Care must be taken so that all connections are stable during flight. This problem may be improved somewhat by installing the components in a rack that can be secured in the cargo space of the aircraft, and by routing and securing the cables. This is only practical if the same aircraft is going to be used throughout the sketchmapping season.

If the same aircraft can be used consistently, other advantages may be realized. Connections to the GPS and power supply in the aircraft could be established, eliminating the need for an external GPS receiver, antenna, batteries, and an inverter. We have developed a portable power supply distribution system that requires installation of a standard

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3-pin XLR plug into the aircraft’s electrical system. Installation of this plug is simple and all aircraft contractors to date have willingly made the installation. These connections could be a specification in the sketchmapping-aircraft procurement contract.

DEMONSTRATION TRIPS

During the past year, we conducted demonstration trips in Hunstville, Texas;

Durham, New Hampshire; Mesa, Arizona, and Roscommon, Michigan. Typically on these trips, we present the system on the first day, conduct flight tests on the second day (and third day if necessary), and discuss/demonstrate post-processing and integration of the data into a GIS on the fourth day. The system was well received by the participants of these demonstrations. Participants included local, state, and USFS sketchmappers. Input from the many sketchmappers that have used the system in-flight have helped us to focus on useful modifications to the software. Systems are currently in place in New Hampshire, Michigan, and Alaska, and a system will be in place in Oregon by the 2000 field season. Additional demonstrations are planned for Salem, Oregon; Anchorage, Alaska, and for forestry personnel in Israel.

During past demonstration trips, the subject of the accuracy of the sketched features was discussed. In the Southern Region (R8), sketchmapping flights are conducted intensively throughout the growing season to locate small outbreaks of southern pine beetle infestation. The goal is to treat these spots before they increase in size. These small areas are typically sketchmapped as points. GIS Technicians “heads-up” digitize these points, and the coordinates are used by the field crews to navigate to the area to assess the damage. The accuracy of these points must allow crews to find the infested areas, which may be as small as three trees.

In order to test the accuracy of points sketched with the digital system, experienced sketchmappers digitized known features such as road intersections and bridges during the flight tests. The resulting coordinates were loaded as waypoints into a GPS receiver, and crews navigated on the ground to the mapped features. These test features were inaccurate from 3 to 500 feet. This was considered unacceptable because locating the infested areas with this much uncertainty would be difficult given the thick undergrowth that is characteristic of the region. Accuracy is especially important when the goal is to treat selected infested areas within 30 days of detection.

We discussed ways to improve the accuracy of the sketched data. Real-time differential correction of the GPS signal is possible but will likely have negligible effects on the accuracy since the points are sketched using ground features that are visible on the background map as reference, rather than points sketched right in the GPS-recorded flightline. National Map Accuracy Standards for the 1:100,000 scale maps used as background data specify that point features may be off by up to 166 feet; thus nearly half of the observed error may be accounted for due to the maps. We concluded that using digital orthophotographic quadrangles (DOQ) (Figure 12) would improve accuracy by providing more features for the sketchmapper to reference than the digital raster graphics (DRG), including existing harvest units and small spur roads.

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Figure 12. Digital Ortho-Photos and satellite imagery can be used as background maps in Geolink PowerMap.

Also, the DOQs would meet the National Map Accuracy Standards for 7.5-minute quads, which corresponds to error of no more than 40 feet for point features. We agreed that the use of DOQs as background data should be investigated. Subsequent tests have confirmed that point features sketched using DOQs as a background map were significantly more accurate that those sketched using the DRGs as a background map.

RECENT ADVANCES We have gained a lot of experience while setting up the system with a variety of

computers, operating systems, and serial adapters. This experience, plus information on preparing background maps from a variety of image sources and data post-processing, has been captured into a “User’s Supplement.” This manual is intended to complement the hardware and software manuals, not replace them.

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REFERENCES

Thistle, H., Greenfield, P., McConnell, T., Myhre, R., and Rankin., L. 1996. Sketchmapping Interim Report. Technical Report No. FHTET 96-31 (Cross reference no. 9634-2855-MTDC). USDA Forest Service, Forest Health Protection, Davis, CA. 40 pp.

SUMMARY/CONCLUSION This project began with a survey of the sketchmapping community, identifying their

needs and concerns. Next, a series of trips were made to investigate currently-functioning systems. The result of these two efforts was a list of the features desired in the first system prototype. After researching available hardware and software options, we contracted for the necessary software modifications and assembled a functioning hardware set-up. Our demonstrations of this prototype system to sketchmappers have resulted in a list of modifications to the system, and we are currently pursuing these modifications. This system is a work in progress, and with each step we are closer to developing a system that will be a tremendous leap forward for aerial sketchmapping.

The cost-saving benefits of this system per Region are estimated to be between $7,000 and $15,000 per year; these savings are primarily in the reduction of time spent post-processing data. Another benefit that is difficult to put a price tag on is quicker delivery of the sketchmap data to the field. In most Regions, there is a significant time lag of 4 to 6 months between the time the data were collected and delivery to the Forest. The digital system would potentially reduce this time lag. Other resource programs such as fire, vegetation management, law enforcement, and wildlife have shown an interest in the system. Any aerial geospatial data collection activity where the data will be placed into a GIS would probably save substantial time and dollars using this system.

The keys to successful development of an application are clear communication with the end-user group and thorough investigation of current and anticipated technology. Through continued clear communication with the sketchmapping community and awareness of available technology, we are confident that we can produce a system that will increase the efficiency and accuracy of aerial sketchmapping.

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