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CALIBRATION PHASE TEST GRID 
  
First, it enables software development to proceed without the necessity 
of observing a model for each test of the program. In addition, the data 
in the test file can be created to simulate certain critical conditions and 
rigorously test the software and check the precision of all the results. 
This technique can also be used as a final check whenever a change has 
been made to a program in the system. It helps prevent unforseen errors 
occurring due to some minor modification elsewhere in the system. 
The third major use is when the software is installed on a new type of 
host computer. There are always some minor idiosyncracies in each different 
computer system and this form of rigorous check allows confidence in the 
installed system. 
(iv) Test grids 
For any customer, the ultimate and most important test is the per- 
formance of the system in the workplace. However this assessment is some- 
what subjective, as every operator is very much conditioned by their photo- 
grammetric background and their experience from using other types of equip- 
ment. In addition, with any photogrammetric job, one cannot find out the 
exact camera orientations, or their positions, and this complicates any 
testing procedure. 
To provide a consistent numerical assessment of performance, it was 
decided to generate a set of test "photographs" numerically, and use these 
for final acceptance tests of each instrument. To provide a reasonably 
demanding test, each photo would have to have significant tilts, the photo- 
graphy should be convergent, and the differences in height between targets 
amount to up to 207 of flying height. 
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