School of Surveying and Spatial Information Systems

University of New South Wales


Combining Terrestrial Laser Scanning and Photogrammetry

by Michael Dodd

Supervisors:  Dr. B.R. Harvey

                           Mr Brian Donnelly

 

October 2003


Introduction

A vast amount of research and commercial work has been carried out using Terrestrial Laser Scanners for High Definition Surveys.  As a result, a large amount of literature has been written about this relatively new technology.  This thesis summarises some of the literature (research papers, journal and magazine articles, trade information such as brochures and seminar material) in a way that will show the principles involved in terrestrial laser scanning, current market availability, laser scanning strengths and weaknesses, future development as well as applications of the technology.  A further aim of this thesis is to continue this work.  An experiment was undertaken to determine whether Terrestrial Laser Scan data can be used as the Digital Elevation Model for the production of an ortho image, for terrestrial photogrammetry applications.  This was performed using the Cyrax 2400 Laser Scanning System and the Photogrammetry package SOCET SET.  A final aim of the thesis was to investigate the potential of displaying modelled Terrestrial Laser Scan data in a Virtual Reality format.

 

 

Literature Summary

The literature consisted of over 110 articles including research papers, journal and magazine articles, trade information such as brochures, press releases, case studies and seminar material.  These articles were summarised under the following broad categories:

1) Laser Scanning Overview - Principles Involved, Registration of Scans, Modelling of Data, Accuracy and Calibration, Intensity

2) Strengths and Weaknesses of Terrestrial Laser Scanning

3) Current Market Availability

4) Applications

5) Future Developments

The literature study highlights the emergence of several exciting new developments in the world of Terrestrial Laser Scanning, in particular, the ability of several newer scanners to present captured data in true colour at a high precision.  For information regarding some of these scanners, view the respective websites of the manufactures:

Leica HDS3000:  http://hds.leica-geosystems.com/en/index.htm

Riegl LMS-Z360i:  http://www.riegl.com

Mensi GS200:  http://www.trimble.com/3D-laser-scanning

 

Measurement Campaign

A measurement campaign was carried out using the Cyrax 2400 with the aim of generating a Digital Elevation Model for the purposes of producing an ortho image from a close-range digital photograph.  A section of the Rupert Myers Building, found on the Kensington Campus of UNSW, was chosen as the object to be scanned for this project.

An exportable DEM was produced in Cyclone v4.  This data was exported as an ASCII file and then imported into SOCET SET as the DEM required for the production of an ortho image.  A digital camera image was successfully oriented using coordinate data captured by the laser scanner.  Production of an ortho image failed as it was not possible to successfully use the DEM to correct for relief displacement.  It was concluded that the reasons for this included the inability of the software to use a DEM containing vertices such as the edge of a building where objects come directly towards the camera.  It was also found to be necessary to remove all object data behind the windows of the building as the software attempted the merge the image onto these objects.  Shadowing caused by objects located between the scanner and the building, such as a large tree, resulted in the DEM being an non-continuous surface  It was further noted that there are currently available Terrestrial Laser Scanning systems capable of generating true colour ortho images.

Visit www.riegl.com for example of producing 3D colour orthophotos using Laser Scanners.

 

                                       Fig 1:  Edited Laser Scan Data                                              Fig 2:  Rupert Myers Building

 

Fig 3:  Distorted image produced as SOCET SET was unable to merge DEM with oriented digital image.  Note that objects coming directly towards the camera and objects behind windows cause distortion.

 

 

Terrestrial Laser Scanning and Virtual Reality

Terrestrial Laser Scanning data is edited and modelled in what is essentially a Virtual Reality world.  Users are able to rotate, pan and zoom the captured data in all directions so as to edit and model the scene, as well as communicate the data in a manner that can be easier to interpret than traditional 2D or 3D CAD drawings.  The ability of these systems to communicate data is significantly enhanced by the ability of several newer scanners to present the true colour of an object, not just the reflected intensity value of the laser beam.

In the case of the viewer not having access to laser scanning software, an alternative method is required to present the data in Virtual Reality.  However, most laser scanning software packages do not readily export data in alternative virtual reality formats.  Two alternative methods of presenting the scan data in Virtual Reality were presented, VRML and OpenView.

For an example of VRML visit - www.parallelgraphics.com/products/cortona/koenigsegg/ (note: it will be necessary to download the Freeware                                                      Cortona VRML Client, found at the same address.  Less than 1min using Cable Internet)

 

Fig 4:  Example of true colour scanning using I-SiTE hardware and software

 

 

Conclusions

Literature relating to Terrestrial Laser Scanning was summarised.  An experiment was carried out to determine whether a DEM generated by a Laser Scanner could be used in the production of an ortho image.  This experiment was unsuccessful.  Finally, methods of displaying Laser Scan data in a Virtual Reality format were presented.

 

 

Useful Internet Resources

I-SiTE 3D Laser Scanning (2004) I-SiTE 4400

Leica Geosystems HDS (2004) Products, http://hds.leica-geosystems.com

Mensi 3D Laser Scanner / 3D scanners for surveying applications (2004) GS200 3D Laser Scanner, http://www.mensi.com

Riegl Laser Measurement Systems (2004) 3D Scanner Selection Guide and 3D Software Selection Guide, http://www.riegl.com

Spar Point Research LLC, online journal related to Terrestrial Laser Scanning 


Further Information

For more information, please contact:

Bruce Harvey (Supervisor)

Email: B.Harvey@unsw.edu.au 

 

Mail:

School of Surveying and Spatial Information Systems

University of New South Wales

UNSW SYDNEY NSW 2052

Australia

 

Phone: +61-2-9385-4202

Fax: +61-2-9313-7493

WWW: http://www.gmat.unsw.edu.au