ON THE PRECISION 
OF 
STEREOMETRIC SYSTEMS 
Dr. H. M. Karara 
Professor of Civil Engineering 
University of Illinois 
Urbana, Illinois 61801 USA 
ABSTRACT 
Even though photogrammetry is ideally suited for on-site 
measurements of objects under test conditions in fields such as 
experimental structural mechanics, the use of photogrammetric 
techniques in such operations has been severely hampered by 
several factors including the need for elaborate camera arrange- 
ments which cannot generally be accomodated in a busy test floor. 
In this respect, stereometric cameras offer a potential solution. 
This paper reviews the current status of stereometric cameras 
and discusses the results of theoretical and experimental 
studies conducted at the University of Illinois to explore the 
feasibility and assess the potentialities of the use of stereo- 
metric systems in conjunction with the measurement of deforma- 
tions of structural models under test conditions. Some of the 
major factors that limit the precision and capabilities of 
current stereometric cameras are reviewed. In the light of the 
results of experimental tests and theoretical investigations, 
definite modifications in the conventional stereometric cameras 
are suggested to enhance the precision of the stereometric 
approaches to meet the high level of accuracy (standard devia- 
tion of spatial coordinates in the order of + 0.005 inch) gen- 
erally required in structural experimental research and in 
several other engineering and scientific fields. 
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