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3-D MEASURING SYSTEMS BASED ON THEODOLITE-CCD CAMERAS 
Yi Dong Huang 
Nottingham Polytechnic 
Department of Civil and Structural Engineering 
Nottingham, NG1 4BU, U.K. 
ABSTRACT 
A 3-D measuring system is proposed which is formed by attaching a CCD camera to the telescope of 
each of two motorized theodolites. This system can work in the same way as other motorized 
theodolite systems but using the mounted CCD cameras as vision devices to search targets 
automatically. It can also work on the photogrammetric principle with the CCD cameras as imaging 
devices and the theodolites as precise direct orientation tools. High resolution image coverage 
can be obtained by capturing serial images while swinging the telescope with the camera attached. 
A function of automated 3-D tracking while measuring can also be incorporated in the system. In 
this paper, the techniques for system calibration and orientation are described and the accuracy 
capacity of the system investigated experimentally. 
KEY WORDS: 3-D; CCD; Theodolite; Calibration. 
1. THE SYSTEM -- THEODOLITE-CCD COMBINATION 
The proposed 3-D measuring system consists of 
two  theodolite-CCD cameras. Each of the 
theodolite-CCD cameras is made by attaching a 
CCD camera rigidly on the telescope of a 
motorized  theodolite. The camera and the 
theodolite are optically independent of each 
other so that the camera can take images and the 
theodolite can still measure angles as usual, 
but both are controlled by the host computer 
with image processor mounted. 
Theodolites have served in geodesy and surveying 
as angle measuring devices for many years. Their 
ability to determine three dimensional 
coordinates is based on the principle of 
pointwise triangulation. They feature very high 
pointing accuracy with a panoramic coverage. 
Modern theodolites have reached the stage of 
motorization, self correction of instrument 
error, high precision and high stability. 3-D 
measuring systems using motorized theodolites 
have been shown, for example, by the Kern SPACE 
system, to be very efficient and useful in some 
industrial sectors (Gottwald,1989). 
CCD cameras used in place of conventional film 
cameras give the technology of photogrammetry 
the possibility of real-time, on-line and 
intelligent automation. The suitability of CCD 
cameras for photogrammetry has been proved by 
many recent researchers. Photogrammetry features 
instantaneous multi-point record and lifelike 
image display. The relative accuracy of digital 
photogrammetry with available CCD cameras is, 
however, lower than that of theodolite methods. 
Combining theodolites and CCD cameras in a 
measuring system will enable the system to 
choose either theodolite methods or 
photogrammetry, whichever is suitable in a 
particular case. The two types of methods will 
complement each other in the system and give the 
system many exclusive features. Such a 
combination has very good prospects as part of 
a universal measuring system or a surveying 
robot. The detailed advantages of the system can 
be appreciated from the envisaged working modes 
as follows. 
Theodolite Scanning Photogrammetry 
  
The CCD camera, rotatable together with the 
telescope of the theodolite, is mounted with a 
long-focus lens to take large scale images 
required by the specified accuracy. The auto- 
theodolite on which the CCD camera is mounted 
rotates as a scanning device so that the CCD 
camera can take a number of images to cover the 
whole object to be measured. The geometric 
relationship among all the images taken on the 
theodolite station can be determined through the 
theodolite readings. 
Having a relatively low accuracy has been the 
main reason why on-line digital photogrammetry 
with CCD cameras cannot replace the film based 
photogrammetry. High resolution CCD cameras with 
standard photogrammetric accuracy capacity still 
cost a great deal. Yet, on the principle of 
theodolite scanning photogrammetry, the proposed 
system can virtually improve the accuracy 
capacity of the CCD cameras to that of the 
theodolites, which could, taking the Kern E2 
theodolites for example, amount to 1/200,000 of 
the object size (Gottwald, 1989). Besides, the 
system retains all the advantages of CCD camera 
photogrammetry. The measured object can be 
recorded patch by patch, which is faster than 
the point-wise measurement adopted in the pure 
theodolite system. 
Discrete Point Coordination with Automated 
Searching 
The system can also be used to coordinate 
discrete targets point by point with theodolite 
intersection the same way as the Kern SPACE is 
used. The superiority of the proposed system is 
that the CCD cameras can act as a pair of 
'searching eyes' with wide-angle lenses. In 
principle, the scene is first imaged by the pair 
of wide-angle cameras and the targets in the 
scene are then detected and located roughly by 
photogrammetry. Finally, the rough three 
dimensional coordinates are used to guide the 
telescopes to point at the targets individually 
for precise determination. In practice, there 
may be various strategies and tactics of doing 
this.