School of Surveying and Spatial Information Systems

The University of New South Wales


Terrestrial Laser Scanning

 

by Jason Raic

 

Supervised by Dr. B. R. Harvey

 

Editted by J. M. Rüeger


The School of Surveying and Spatial Information Systems purchased a terrestrial laser scanner (Cyrax 2400) in January 2001. The Cyrax 2400 system was used to carry out experiments, establish procedures and perform tests on the system.


Merging Images

The process of the merging of images was tested first, by scanning a pole from two positions. Using only a fitted cylinder to the pole, along with a common coplanar patch on the ground, there were insufficient constraints for the merging algorithm to form an initial joining guess, as expected. The images could not be merged together because the geometry of the common objects was not good; the images would have been spinning about the pole. Secondly, two scans were taken to capture the Red Centre Building shown in Figure 1. Using only common planes and cylinders, the scans were easily and successfully registered together. This time there were sufficient constraints and the geometry of the objects allowed a successful registration. The careful positioning of targets was the common method used to join images together. However, the results from this test show that the images can be joined together, without loss of accuracy, without targets.

 


Figure 1:
Final  image of the Red Centre Building on the UNSW Campus

 

Walk-Through

A walk-through of the image in Figure 2 was produced. In the movie, it seems that one is walking through corridors and turning around corners. To make the walk-through, nine scans were taken from three positions and then joined together using targets and planes. With the final image consisting of all the joined scans, the AVI software was used to make a movie of the scanned area. The AVI software captures operations carried out on the screen, in this case, zooming in and panning. Details (such as papers on notice boards, a garbage bin and a fire hose) were captured and are seen in the movie. To view the walk-through, download walk-through. (This could take about 30 minutes to download over a 33k modem.)


Figure 2:
Area captured for the production of a walk-through. Situated on the fourth floor of
the Electrical Engineering Building on the UNSW Kensington Campus.

 

Refractivity Effects on Cyrax Laser Distance Measurements

The refractivity effects on Cyrax 2400 laser distance measurements was calculated. A number of trends where observed. Over 100 m, an increase in atmospheric pressure leads to an decrease in the first velocity correction (3.6 mm from 960 hPa to 1050 hPa) and an increase in temperature leads to an increase in the first velocity correction (4.3 mm from 0C to 45C). (Clearly, the Cyrax 2400 should have a facility to correct for temperature and pressure effects (ed).)

 

Other Experiments

Some deformation measurements were taken, testing the accuracy of the Cyrax 2400 measurements. Also, the coordinate origin of the Cyrax 2400 (the mechanical axes being offset from the coordinate origin) was determined approximately.


Further Information
For more information contact:

Dr. B. R. Harvey (Supervisor)
B.Harvey@unsw.edu.au

Mail:
School of Surveying and Spatial Information Systems
University of New South Wales
UNSW SYDNEY NSW 2052
Australia

Phone: +61-2-9385-4178
Fax: +61-2-9313-7493
WWW: http://www.gmat.unsw.edu.au