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DIGITAL PHOTOGRAMMETRY IN INDUSTRIAL APPLICATIONS 
Horst A. Beyer 
IMETRIC SA 
Rue du Bourg 9 
CH-2892 Courgenay, Switzerland 
KEY WORDS: Digital 3D Image Metrology, State-of-the-Art Systems. 
ABSTRACT: 
Real-time photogrammetry has evolved from a R&D topic to a technique successfully applied in a number of fields. Among the many 
cameras available for real-time photogrammetry still-video cameras have proven to be ideally suited for most tasks. They are easy to 
use, provide for a large storage capacity, have sensors with up to 3072 x 2048 elements and can even be used as on-line cameras. 
Systems using these cameras have found acceptance in a number of application areas. The paper reports on results obtained with the 
IMETRICS TP210 and TP250 system series. Accuracies of 1/100th of the pixel spacing are obtained by users of the systems. Relative 
accuracies of 1 part in over 100 000 are obtained in every dày use. Relative accuracies of 1 part in 168 000 have been verified and 
repeatabilities of 1 part in over 200 000 have been demonstrated, employing modified Kodak DCS420 cameras. 
1. INTRODUCTION 
Digital 3D image metrology has evolved over the past several years, from a R&D topic (see for example Gruen and Beyer, 1987) to a 
tool used in many sectors. This rapid change is in part due to the dramatic advantages this technology has over other measurement 
techniques such as film based photogrammetric systems, industrial theodolites and laser trackers. The speed with which data can be 
captured and processed allows for the minimization and even elimination of any interruption to the production processes. Faster feed- 
back allows for better control of production and for elimination of parts or products that are out of specifications. These are 
determining factors in today's extremely competitive economic climate. 
Prerequisites for the existence of systems integrating these technologies were: advances in CCD sensors, such as the number of sensor 
elements and sensor quality; as well as improved algorithms allowing for higher accuracy, improved robustness and automation. 
This paper presents the state-of-the-art in metric accuracy performance of digital 3D image metrology or real-time photogrammetry 
systems. The results presented are drawn from the many tests that have been undertaken with the IMETRICS systems over the last 
years. These tests were performed in almost every application area stretching from aerospace to the medical field. The tests were part 
of system demonstrations, acceptance tests, standard system use and pure accuracy verifications. Using modified still-video cameras, 
accuracies of 1 part in 150 000 in object space have been achieved and validated. Repeatabilities of 1 part in 200 000 in object space 
and image coordinate precisions of 1/100th of the pixel spacing have been attained by users of such systems. 
2. CAMERAS 
System developers and users can find a large variety of cameras on the market that are more or less suited for 3D image metrology. 
These include standard industrial inspection cameras, video cameras, “high resolution” cameras, still-video cameras and 
“photogrammetric” cameras. 
Standard inspection cameras have the advantage of low cost and fast image frame rates. However, they provide insufficient accuracy 
for many industrial tasks. Video cameras have a tremendous integrated storage capability but have even worse accuracies than 
standard industrial type cameras. A number of “high resolution” cameras with area array sensors up to 2000 x 2000 pixels are 
commercially available. These generally need a frame grabber with the associated cable connections. While image data can be 
transferred at rates of 10 Mbytes/sec and higher, the cables render them cumbersome for many tasks. 
Still-video cameras that provide both an integrated storage and a direct computer link represent the most promising type of cameras 
currently available. Some applications with still-video cameras can be found in for example Beyer (1994), Maas and Kersten (1994) 
and Peipe et al (1994). With the large size of the still-video camera market and emerging competition, better cameras at lower cost 
will become available in the future. Typical examples of still-video cameras are the Kodak DCS range. Currently, the range includes 
the Kodak DCS420 and DCS460 cameras as well as the DCS465 camera back. The DCS420 camera (see figure 1) has a sensor with 
IAPRS, Vol. 30, Part 5W1, ISPRS Intercommission Workshop "From Pixels to Sequences", Zurich, March 22-24 1995