THEORETICAL DETERMINATION 
OF THE MAXIMUM BRIDGING DISTANCE 
IN AEROTRIANGULATION PROJECTS * ** 
Dr. H. M. Karara, USA *** 
The density of ground control is one of the main parameters upon 
which the accuracy of aerotriangulation is contingent. The quality of 
photogrammetric control, deduced through aerotriangulation, governs the 
accuracy of any consequent photogrammetric mapping and therefore deserves 
utmost consideration. 
As one can expect, the accuracy of photogrammetric control is 
bound to be somewhat lower than that of terrestrially determined ground 
control. To ensure a specified accuracy in photogrammetric control, 
the bridged distance has to be confined within certain limits. In case 
of a long strip, it may not be sufficient to have ground control only 
at the beginning and end of the strip, as indicated in almost all text 
books of photogrammetry. Referring to Figure 1, some sort of ground 
control has to be established at intervals (referred to here as Maximum 
Bridging Distance 'mbd') throughout the long strip. 
Figure 1 mbd = maximum bridging distance 
* Presented at the Tenth Congress of the International Society of 
Photogrammetry at Lisbon, Portugal in September 1964 (Commission 
hi). 
** This paper summarizes part of the work done in a research project 
sponsored by the National Science Foundation (NSF G 19749)* 
*** Associate Professor of Civil Engineering, University of Illinois, 
Urbana, Illinois, USA.