of Surveying and Spatial Information Systems
University of New South Wales
of Industrial Measurement Techniques
Supervised by B. Donnelly
by J. M. Rüeger
Edited by J. M. Rüeger
The term Industrial Measurement Techniques can be applied to a wide variety of image acquisition and image analysis methods. The two techniques researched were the Cyrax 2400 Laser Scanner and Digital Close Range Photogrammetry. The aim of this project was to examine which of these two technologies is the more appropriate for the measurement of industrial objects. To compare these two technologies, a small boat was measured with both techniques.
Terrestrial close range photogrammetry has been used to
measure large irregularly shaped objects such as ships and aircraft for many
years. The new technology of 3D
laser scanning can also be used to measure such objects.
For this project, a comparison was made between these two technologies
using literature sources and a practical measurement using the School of Surveying
and Spatial Information System's Cyrax 2400 3D laser scanner and digital photogrammetry
with a Kodak DC260 digital camera. Incorporated
into the learning of the two measurement techniques were their associated software.
For the laser scanner the Cyclone software was used and for the close
range digital photogrammetry the Australis software package.
DC260 Zoom Camera
Several key aspects of the equipment and post-processing steps, that are used in combination to produce 3D data for the exportation to CAD software, were compared for these two image-capturing devices. The most important aspects to consider are the following:
For the experiment, a Kodak DC260 zoom digital camera, pictured in Figure 1, was used. It has a resolution of 1536 x 1024 pixels per image when used in best quality mode.
The Cyrax 2400 laser scanner is
a high speed, 'high accuracy' laser radar scanner.
The scanner is operated from a laptop PC and features an integrated video
camera. Its point position accuracy at maximum range (100 m) is ±6
The Cyrax 2400 Laser Scanner uses a pulsed green laser with a central
wavelength of 532 nm. The angular
field of view of the Cyrax 2400 is 400 in the vertical (± 200
from the horizontal) and 400 in the horizontal.
Figure 2 shows the Cyrax 2400 Laser Scanner in operation.
Cyrax 2400 Laser Scanner
Eighteen digital images were
taken with a Kodak DC260 zoom camera for the digital close range photogrammetry
experiment. The digital images
were imported into the Australis processing software and a least squares bundle
adjustment was performed. The Australis
bundle adjustment gives a list of the XYZ coordinates of the retro-reflective
targets on the boat. Figure 3 is
a sample of the images gathered in the experiment.
A total of three scanner locations were used for the scanning of the boat. This resulted in three 3D point clouds that could be used to produce a 3D model of the boat. It was possible to carry out the merging ('registration') of the three point clouds in the field. It took only thirty minutes to merge the three clouds and to produce the final 3D point cloud model. Figure 4 below shows a screen capture of the 3D model of the boat.
Sample image from digital close range photogrammetry experiment.
The field time required for
the acquisition of the boat data was compared between the techniques.
The laser scanning of the boat took four hours, compared to two and a half hours
for the photogrammetric measurements
measurements. For the post-processing of the acquired data, half an hour was spent on the laser scanning and 10 hours on the photogrammetry. The Cyrax targets, that were common to both data sets, were used to compare the two results. Using the coordinates of the targets from both methods, the inter-target distances were calculated. The differences ranged between two and ten millimetres.
This project allowed a comparison between two relatively
new techniques of industrial measurement. Both gave accurate results of the
measurement of a boat. When determining
the best measurement technique for industrial measurement, a combination of
the features of the two techniques must be compared. Time and cost are two major
considerations to be looked at. If
cost is no obstacle in a project where accurate XYZ point coordinates are needed
then the Cyrax 2400 Laser Scanner is far superior to digital close range photogrammetry.
However, when using the (relatively) cheaper digital camera (with a bundle
adjustment software), a better accuracy can be obtained, at the expense of lengthier
One of the most important distinctions to be made between the two techniques considered is the amount of 3D data acquired by each technique. Laser scanners acquire thousands of points over the field of view in a very short period of time. When several scans are merged, the resulting 3D point cloud gives a detailed, useable 3D model of the object's surface. A major difference with digital close range photogrammetry is the number of 3D points that can be acquired. Digital photogrammetry can only acquire 3D coordinates of points on an object that are marked with retro-reflective targets. This puts a limit on the number of points acquired on an object, and the detail that can be displayed in 3D models.
Figure 4: 3D point cloud model of the boat
For more information, please contact:
Brian Donnelly (Supervisor)
School of Surveying and Spatial Information Systems
University of New South Wales
UNSW SYDNEY NSW 2052