Zlatan Novak

Vektra d.o.o., Geo3D d.o.o.,

Antuna Mihanovića 6a, 42000 Varaždin, Croatia

e-mail: vektra@vektra.net, zlatan.novak@geo3d.hr

web: www.vektra.net, www.geo3d.hr

LIDAR and 3D Laser Scanning – Bringing the Pieces of History Back Together

Introduction

Geodesy is a branch of earth sciences. It is the scientific discipline that deals with the

measurement and representation of the Earth and objects, including its gravitational field, in a three-

dimensional time-varying space. This scientific discipline has a wide variety of appliances and works

in collaboration with many other sciences and practical uses.

As a technical science of applied mathematics and physics it quickly grew with regards to

developments in informatics. The need for representation of Earth surface, spatial data processing and

analyzing, is constantly growing and takes place in every aspect of technical and social development.

The need for faster, more detailed, precise and accurate representations of the spaces and

objects as virtual reality, becomes a great challenge in the development of spatial data acquisition

systems. The following examples will show some of the unique projects and outstanding technical

achievements in 3D spatial data acquisition and imaging.

Our project samples are related to the use of two sophisticated 3D laser scanning systems.

Optech ILRIS3D was developed by a Canadian company which was the first to start with the

development of the LIDAR systems. LIDAR, or Light Detection

and Ranging, is a technology on which the systems described in this

article are based. The ILRIS3D system is a TOF (Time of Flight)

measuring system. In other words it measures the time needed for

the laser pulse to hit the object and return to the receiver. Therefore

the LIDAR systems basically consist of a laser transmitter and

receiver. What makes it so expensive, complex and sophisticated is

its ability to gather thousands of points in one second with high

accuracy, small point spacing (resolution) and long dynamic range.

One of the systems we used is the most versatile system of its kind

in the world. With its ability to acquire data from 3 to more than 1,500 m at a speed of 10,000 points

per second the system can be used in a great variety of applications.

Figure 1. The same system used in applications described later in this article will be the first system used

to acquire 3D spatial data of the Moon. (NASA Ames K10 Rover with Optech ILRIS3D scanner on top)

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Principle of LIDAR

Laser + Receiver System = Lidar (Light Detection and Ranging)

Laser radar depends on knowing the speed of light, approximately 0.3 meters per nanosecond. Using

that constant, we can calculate how far a returning light photon has traveled to and from an object:

Distance = (Speed of Light x Time of Flight) / 2

1. Laser generates an optical pulse.

2. Pulse is reflected off an object and returns to the system receiver.

3. High-speed counter measures the time of flight from the start pulse to the return pulse.

4. Time measurement is converted to a distance by using the formula above

Knowing the distance and the angle between the fired laser beam and the certain zero

angular position, trigonometry can be applied to calculate the spatial coordinates of each single point.

The points are recorded in a three dimensional coordinate system known as a Cartesian coordinate

system. It is a rectangular coordinate system with X and Y coordinates defining the position and a Z

coordinate representing the height of the point. The origin of the model is in the center of the laser

transmitter (unless otherwise defined), but it can be transformed into any other coordinate system

depending on the use of other measurement devices and reference coordinate systems. To simplify the

principle again, a 3D laser scanner fires thousands of laser shots per second and every shot becomes a

3D point of the object it hits. When looking at the raw data it appears as a solid 3D model of objects

and spaces as the points are very close one to another. Therefore, they automatically present a very

realistic and precise 3D model.

The second system we used is much faster and closer range based with the ability to get sub

millimetre accuracy. Unlike the TOF scanner this system uses a different principle, but again measures

the distance that every laser pulse makes travelling from the transmitter to an object and back to the

receiver. Beside the time of flight principle, the phase measurement principle is the other technique for

close and medium ranges. The high acquisition rate and high density of 3D points are the peculiar

characteristics of phase-shift systems. The system we use and the data shown later in this article come

from a Z+F Imager5006i 3D scanning system produced in Germany. These two systems have proven

to be a very good combination as they both represent the state-of-the-art technology in their domain.

This allows them to take on all the possible challenges in terrestrial 3D laser scanning tasks.

The 3D imaging LIDAR systems develop quickly and enter new dimensions of spatial data

acquisition. They are not used only as terrestrial static systems, but also for dynamic airborne, mobile

and underwater acquisition for applications which need different sensor fusions and integrated

customized systems. Those systems are used on airplanes or helicopters, marine vessels and cars as

rapid mobile mappers etc. The systems, static or mobile, are used in the fields of; architecture, urban

planning, archaeology, cultural and natural preservation, commercial survey, geology, public safety,

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engineering, mining, industrial markets, forensics, military and all other applications where there is a

need for precise virtual reality in the form of a measurable 3D model.

This article will mostly concentrate on the use of 3D laser scanning technology in cultural and

natural preservation tasks. Every environment with valuable historical buildings can be recorded and

stored in detailed ways like never before. Complete reliable reconstructions can be made, and cultural

heritage can be preserved in a digital authentic manner. Every archaeological excavation can be

studied in an office as if the scientist were out in the field simply by walking through his research area

digitally on his computer. This 3D model of existing objects allows the extraction of all technical

features such as orthogonal cross-sections in every desired position on the object. All the spatial

analysis can be made thanks to the highest level of details. Architecturally extracted charts from a

precise 3D model can reveal all the possible deformations and hazards important to the reconstruction

project design.

Figure 2. The Optech ILRIS3D system on the top of Lotrščak tower in Zagreb during work at the

archaeological excavation site

Archaeology

3D model of the Church of the Blessed Virgin Mary in Remete near Zagreb

The first Pauline monastery in present-day Croatia was founded in the second half of the 13th

century on the lower slopes of the Medvednica Mountains. During two seasons of archaeological

excavations (2007 - 2008) on the southern plateau of the parish church of the Blessed Virgin Mary, the

ruins of two earlier churches were discovered. The massive foundations of both churches were heavily

destroyed as a result of geotectonic disturbances. The older church (mid-13 century), was destroyed

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only a century after it was dedicated, due to the earlier mentioned geotectonic disturbances. However,

the Paulines decided to build another church on the same ground. During the 15th century, the church

sustained great damage, again as a result of geotectonic disturbances. Yet again, a new church (the one

currently standing), with a monastery complex was built using the foundations of the two previous

churches for support.

Since the foundations were greatly damaged and shifted towards the southern and eastern

slopes of the plateau, reassembling for proper interpretation was needed. Laser scanning has been

shown to be the only method possible for the precise reconstruction of the damaged foundation

“puzzle” of the churches. Optech’s ILRIS-3D laser scanner and 3D data analysis methods helped

reconstruct this middle-age puzzle with its outstanding characteristics and versatility. It helped in

proving the geometrical facts of two historical churches and bringing the broken pieces of history back

together. With an operating range of from 3 m to more than 1,500 m the ILRIS-3D offers a complete

solution for archaeological research combining the closer smaller objects with its geographical wider

area. The pictures below show the principle of joining moved parts.

These precise charts were extracted after processing the spatial data acquired with the 3D laser

scanner. The data processing consisted of CAD technical drawings, 3D polygonal mesh modeling, and

finally animation of the foundations. The animation showed the joining of the parts moving into their

original positions and raising the original shapes of the two middle-age churches. All the data was

geographically transformed into the national mapping grid allowing for future upgrading of the model

after new excavations but also to overlap the data with existing topographical charts etc. Among other

final deliverables, the cross sections were also extracted and finalized in CAD environment.

Figure 3. Church of the Blessed Virgin Mary in

Remete – Geo-referenced 3D model represented as

the RGB detailed point cloud

Figure 4. Zoomed detail of the Geo-referenced 3D

model represented as the RGB point cloud showing a

high level of details with measurable functions

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(a)

Figure 5. a) Precise CAD drawing of both church

foundations on their discovered location. b) CAD

reconstruction of one of the churches based on the

detailed information extracted from the 3D scanned

data

(b)

(a)

(b)

Figure 6. a) Final part of the animation with reconstructed foundation of the both discovered churches in

respect to the existing church presented as a solid polygonal mesh 3D model generated from the 3D laser

scanner data. b) Animation of joining the foundation parts for the older church (13ct)

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Neanderthal Site of Vindija Cave near Varaždin

Vindija Cave is a stratified archaeological site in Croatia, home to several settlements

associated with both Neanderthals and Anatomically Modern Humans (AMH).

Vindija includes a total of 14 levels which date to between 25,000 and 45,000 years ago,

spanning the Middle Paleolithic and Upper Paleolithic periods. Although several of the levels are void

of hominin remains, or have been disturbed by burrowing animals or ice wedging, there are four to

five stratigraphically separated hominin levels at Vindija Cave associated with humans and

Neanderthals.

The site was first excavated in the late 19th century, and more extensively excavated between

1974 and 1986 by Mirko Malez of the Croatian Academy of Sciences and Art. In addition to extensive

archaeological and faunal remains, remains from over 100 separate hominins have been found at

Vindija Cave.

As a result of new 3D laser scanning technology we created a project related to this valuable

archaeological site. The raw precise model of the exterior and interior of the cave has a

multifunctional purpose. First of all there was an immediate need for preserving the cave from future

devastation. From an architectural point of view some elements of construction had to be fitted into

this natural site. For instance, a protective rail fence had to be designed. Since every rail had to be

different, due to the natural stone diversity in longitudinal and cross sectional lines, a complete and

precise 3D model from a 3D laser scan was the best way to go about it. After recording every cm of

the cave as a detailed 3D model, other analysis was possible. Geologists, archaeologists, architects and

speleologist were just some of the experts that gained interest in this detailed 3D model. The model

can also serve as a 3D model basis in a 3D GIS data base with all the significant information applied

to the 3D environment for every interesting part of the cave. Periodical 3D scanning and analysis of

the same cross sections can show what is happening to the cave in geological and geographical sense.

The animations and simulations can be perfectly visualized with help of the raw model etc. These are

just some of the possible applications of this technology and project result.

The pictures show; raw 3D model as an RGB point cloud, processed polygonal mesh model of

interior with the possibility of feature extractions such as measurements, angles, elevation error maps,

DEM (Digital Elevation Model), topographical charts of the interior and exterior with contour lines,

orthophoto of the main entrance. These are all the final deliverables and final products that can be

produced after acquiring a complete 3D spatial data model with a 3D laser scanner.

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(a)

(b)

(c)

(d)

Figure 7. a) Vindija Cave entrence – Geo-

referenced 3D model represented as the RGB

detailed point cloud. b) Ortophoto overlapped with

CAD polylines presenting an orthogonal view on

the main cave entrance. c) Cave floor with cross

sections. d) Complete cross section extracted from

the complete polygonal mesh 3D model.

e) Topographical chart of the cave interior and

exterior with contour lines - all extracted from the

3D laser scanner data

(e)

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Plitvice lakes national park – Krčingrad fort

The remains of the fort Krčingrad lie on a plateau between two lakes - Kozjak and Gradina in

the Plitvice lakes national park. The burgh was built in the 14th century for the powerful Babonić

family, but it was abandoned as the Ottoman attacks grew stronger in the middle of 16th century.

Excavations of Krčingrad began in 1911, but they lasted for only two seasons, and they were

not continued until 2008. The fort was encircled with defensive walls, and had two defense-towers on

the southern part and (probably) another one on the northern side. The bigger of two southern towers

is especially interesting because of its rare, triangular ground-plan.

The partial excavations of this unique triangular fort tower took place in the summer of 2009.

A detailed 3D model was created using the phase shift 3D laser scanner. The 3D model will be used

for future geometrical study and CAD technical documentation. The solid 3D model will also be used

for 3D animations and presentations. Because of the diverse and irregular architectural elements of

these ancient historical elements and their remaining scattered parts, and the significance of the high

level of details, a 3D laser scanner offers the best solution for such tasks.

Figure 8. Scanning the Krčingrad fort with Z+F Imager 5600i 3D phase shift laser scanner

Plitvice lakes national park - Corkova uvala virgin forest

Within the Plitvice Lakes National Park, a most beautiful Dinaric jungle - the Corkova uvala

virgin forest has been preserved. This virgin forest is located in section 1 of the forestry area of the

same name, and expands some 79.50 ha. That is primeval, untouched beech and fir forest (Abieti -

Fagetum dinaricum Ht 38) that is growing extensively under the natural conditions of its living space,

without man’s direct influence. A few trees have been cut, in order to make small boards (shingles)

used to cover houses which do not disturb the virgin forest structure. In the Corkova uvala virgin

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forest, all the development phases of European beech and fir virgin forest can be found. Depending on

the quality of living space, or rather on the amount of soil, fir and juniper have lived in karst areas for

more than 700 years and beech for 300 years.

47% the Corkova uvala virgin forest is comprised of beech trees, while 40% are fir and 13%

juniper. The tallest tree there is a juniper - over 50 meters high, followed by a fir of 47m and finally a

beech of 35m. The largest fir tree has a diameter of 140 cm, juniper 130 and beech 102 cm. The

average tree volume in the virgin forest is 565 m3/ha, while in an experimental area which is presently

growing - old phase, the average tree volume makes 1 000 m3. The experimental area mentioned was

chosen in 1957 for forestry research.

The previous paragraph mentions a lot of information related to spatial data analysis. The idea

of having a digital model of the forest research area as a virtual measurable reality in a computer was

something that interested the forest research experts. If we imagine extracting the volumes (radius) of

trees, studying their mutual spatial position, angles of the branches, their vertical deviations, the

volume of tree tops, we are looking at the technological achievement of 3D laser scanning technology.

Manual and conventional methods of gathering that information were time consuming, and in the end

the amount of data and their accuracy and precision was surpassingly poor in comparison to a 3D laser

scanning model. Once again the model was presented in a precise National Mapping Grid which is

very important due to the periodical study of virgin forest transition. The appropriate software solution

for this interactive feature extraction was applied in order to achieve the forest expert’s needs. Once

again the benefits of this technology showed the significance of 3D spatial data acquisition in the

forestry science.

(a)

(b)

Figure 9. a) Plitvice lakes national park, Corkova uvala virgin forest – 3D model point cloud data analysis.

b) Field work in the Corkova uvala virgin forest with Optech ILRIS3D long range laser scanner

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3D models of large areas

Detailed 3D model of the island Veliki Kornat

It has been two years since the worst firefighting tragedy in Croatian history took place. It was

a tragedy in which twelve firefighters lost their lives. This unfortunate event brought together a group

of scientists from various fields of expertise in order to find out what really happened. The leading fire

experts from other countries gained interest in this tragedy as they had recently experienced similar

phenomenon, which they called “eruptive fire”.

The investigation required a detailed and precise 3D model of the canyon between the two

hills on the rocky island of Veliki Kornat. It was a great challenge because the area of approx. 50ha

needed to be scanned in a short period of time. The project organization was limited to a period of one

day because of poor weather conditions (wind and rain) and special transportation that could be

provided for only two days. There was a need for fast, accurate, and long-range scan capabilities, with

no chance of repeating the procedure. The Optech ILRIS 3D terrestrial laser scanner was the best

available solution for such task.

Once again a detailed 3D model of 50ha was used for its various uses. The model was

significant as a 3D data base with all the important forensic positions in a National mapping grid with

precise mutual spatial positions. As a 3D GIS the data base had the proper annotations and information

for each specific position with the possibility of interactive data analysis on the virtual 3D scene.

Furthermore, the 3D model was used in a specific program application for the simulation of natural

conditions. Topographical contour lines were extracted together with a DEM (Digital Elevation

Model) error map making a visual interpretation of the terrain relief. The complete authentic 3D

animation and forensic reconstruction was based on the 3D spatial data acquired with a 3D laser

scanner and later data processing.

The 3D model became the key element in further scientific and practical study of the fire

phenomenon. All of these efforts were made in order to prevent such tragic events in the future.

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Figure 10. a) Complete final high resolution 3D polygonal mesh model of the 50ha of the Veliki Kornat

island canyon made out of data acquired with the Optech ILRIS 3D laser scanner. b) Zoomed part of the

high detail 3D model. c) Photograph showing the high detail level of 3D model achieved with the laser

scanning technology

Figure 11. Optech ILRIS3D scanner on the Veliki Kornat Island – Kornati national park

Conclusion

Both laser scanner instruments and 3D data software are in continuous development. The

Partner companies Vektra d.o.o. and Geo3D d.o.o. from Varaždin made the technological upgrade in

the direction of exploring and implementing new 3D spatial data acquisition methods based on LIDAR

(a)

(b)

(c)

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technology. The technology is still new and it takes time to educate and encourage the market to

accept the new dimensions of 3D laser scanning data representation and collect the benefits, both

economic and practical. The samples used in this article are real projects that show that the market is

ready, followed by fact that all the deliverables were well accepted and made significant push in

comparison to conventional surveying methods. After long and exhaustive development in innovative

data processing methods, constant hardware, software and system investment, experience showed that

clients recognize the benefits while the types of project repeat. Because of its technological

characteristics and benefits it marks a new era in an important segment of 3D spatial data

management.

Acknowledgement

The hardware and software systems and data used for this article were provided thanks to the

partner companies Vektra d.o.o. and Geo3d. d.o.o. from Varaždin.

References

1. FIG COMMISSION 2 workshop „Navigating the Future of Surveying Education“, Vienna,

AUSTRIA, FEB 26-28, 2009.

2. Fröhlich C., Mettenleiter M. (2004): Terrestrial Laser Scanning - New Perspective in 3D Survey.

Proceedings of the ISPRS working group VIII/2.

3. Heine E., Santana Quintero M., Van Genechten B. (2009): ICT-supported learning and training

tools for terrestrial laser scanning applications. In: FIG Comm.2 and Austrian Society of

Surveying and Geoinformation (Eds.), Proceedings of the WG2.3 workshop "Navigating the

Future of Surveying Education"., Digital document (PDF); p.119-123.

4. Lerma García J.L., Van Genechten B., Heine E., Santana Quintero M. (2008): Theory and

practice on Terrestrial Laser Scanning. , pp. 261; Editorial de la Universidad Politécnica de

Valencia., Valencia, SPAIN.

5. Santana Quintero M., Van Genechten B., Heine E., Lerma García J.L. (2008): Learning tools for

advanced three-dimensional surveying in risk awareness project (3DRiskMapping). Final report.

Leonardo da Vinci Programme of the European Union., 34.

6. URL 1: http://www.optech.ca

7. URL 2: http://www.vektra.net

8. URL 3: http://www.geo3d.hr

9. URL 4: http://www.zf-laser.com

10. URL 5: http://www.np-plitvicka-jezera.hr/eng

11. URL 6: http://archaeology.about.com