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Ali, Mahmoud El Nokrashy 
  
3. ANALYSIS AND RESULTS 
3.1 Introduction 
In establishing a GIS for a certain area using MMS, the exterior orientation parameters of the two camera stations can 
be calculated from the GPS and INS data. The GPS gives coordinates of camera stations. Rotation parameters can be 
determined using the INS or different technologies (Thrwat, 1996). Because non-metric camera was used, camera 
exterior orientation parameters could not be determined. Since in MMS the camera exterior orientation parameters are 
known and to have the same condition in our system, a group of control points were used to estimate these parameters 
through a resection for each photograph separately. The number of unknowns for each stereo pair are six exterior 
orientation parameters for each image, focal length, two (x, y) coordinates for the principal point, and six additional 
parameters to correct for systematic distortions as recommended for the used computer program. Hence, the total 
number of unknowns is given as: 
„= 2*6 +1+2+6 = 21 (1) 
Consequently, the minimum required number of equations would be 21 for each stereo pair. The closest, average and 
fareast object-to- camera distances were 30,40 and 50 m, respectively. The average distances (Av-D.) between the 
stereo pair and checkpoints were calculated as follows: 
Av-D. =(dmax +dmin) /2 (2) 
where: 
dmax-— The distance between farest check point and stereo pair 
dmin.......... The distance between closest check point and stereo pair 
To evaluate the results of the tests, the average errors for check points coordinates (SX, SY, SZ) were calculated 
according to the following equation: 
n 
SX=1/n ) ABS (Xp -Xpi ) (3) 
i=] 
and similar equations for SY and SZ. The average error in the total direction 
ST ./S8x SY. S7 (4) 
Where : 
SX, SY, SZ and ST...... average error for the check points in X, Y, Z and T directions respectively. 
Xt V6: Zn Object - space coordinates of point i calculated by field survey. 
Xpi- Ypi. Zpi EHER Object - space coordinates of point i calculated by photogrammetry. 
Boden iBank, Number of check points. 
Since the main objective of this paper is to study the effect of some factors on the accuracy of mobile mapping, several 
tests have been carried out. Abbass thesis (1996) has the detailed of all the tests and their results and analysis. In the 
following sections some of these tests and their results will be given. 
3.2 Effect of Number of Control Points 
The first test was carried out to determine the ultimate number of control points, which gives the best accuracy for 
object - space coordinates. A stereo pair of 2.05m base line was chosen. The number of the points measured in this 
model was 24 points. The model has been adjusted several times using 3, 4, 5,......... ,12 control points. The average error 
for the rest of the points which are consider as check points were calculated using equations (3&4) 
  
International Archives of Photogrammetry and Remote Sensing. Vol. XXXIII, Part B5. Amsterdam 2000. 19