Ali, Mahmoud El Nokrashy 
  
Table (1) illustrates values of SX, SY, SZ and ST for check points, against number of control points. It can be seen that 
values of average errors for check points decreases with increase in the number of control points to a certain limit, then 
it becomes constant. This limit is found to be 9-control points.. Consequently, this number of points will be used for all 
the tests when studying the other factors influencing the accuracy. 
3.3 Evaluating the Accuracy of MMS 
To evaluate the accuracy of the photogrammetric system, a test using six stereo pairs was carried out. All of the models 
have same base line length of 2.05m. From the 33 known points available in the test field 9 points were used as control 
and 12 points as check points. These points were chosen because they appear in the photos of all the tests. 
Table (2) shows the relation between SX, SY, SZ and St and the Av.D. For all models. It is clear that the average errors 
of check points in all directions are directly proportional to the average object to camera distances. The maximum 
average errors are in Z direction for all the models while the average errors for X and Y directions are nearly equal. 
Table (1) Average Errors Against Number of Control Points. 
  
  
  
  
  
  
  
  
  
  
  
  
  
  
No. of Control Average Error (cm) 
Points SX SY SZ ST 
3 6.23 5.63 9.56 12.72 
4 4.86 4.53 8.35 10.67 
5 4.35 4.02 7.87 9.85 
6 4.12 3.74 7.48 9.32 
7 3.91 3.43 7.19 8.87 
8 3.67 3.30 7.05 8.61 
9 3.54 3.24 6.95 8.45 
10 3.61 3.22 7.03 8.53 
11 3.56 3.29 7.18 8.66 
12 3.60 3.21 7.11 8.59 
  
  
  
  
  
Table (2) Average Errors Against Average Objects Distances. 
  
  
  
  
  
  
  
  
Stereo Average Objects Average Error (cm) 
Pair Distance (m) SX SY SZ ST 
1 55 4.30 3.70 8.20 9.97 
2 50 3.92 3.51 7.76 9.38 
3 45 3.63 3:32 7.31 8.81 
4 40 3.54 3.24 6.95 8.45 
5 35 3.33 3.13 6.63 8.05 
6 30 2.87 2.71 6.26 7.40 
  
  
  
  
  
  
  
  
3.4 Effect of Base Line Length 
Many photogrammetrists studied the effect of B/ H ratio on the accuracy of object -space coordinates. It is known that 
increasing base line length means bigger B/H ratio. This will lead to higher accuracy of object -space coordinates. In 
this paper, a base line of 1.8 was selected and an increase of 0.25 m was added to it, until the final base line length 
reached 3.05 m. All models have closest and fareast object-to-camera distance of 30 m and 50 m, respectively. Nine 
points were used as control and 12 points as check points. 
  
20 International Archives of Photogrammetry and Remote Sensing. Vol. XXXIII, Part B5. Amsterdam 2000. 
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