Ebrahjm, Mostafa Abdel-Bary 
  
An orthoimage related to the flat ceiling plan as a reference plan has been obtain directly from the used photogrammetric 
software as shown in figure (5). This image has been divided into four quadrant for purposes of the geometric 
comparison. Each quadrant has been enhanced through an image enhancement software to prepare the images for the 
comparison. The upper-left quadrant is remain as it is, the upper-right quadrant has been flipped horizontally, the lower- 
left quadrant has been flipped vertically and the lower-right quadrant has been flipped vertically and horizontally. Figure 
(6) shows the various quadrates. 
  
Figure (5) An orthoimage of the test field Figure (6) The orthoimage four quadrate 
In the enhanced image which illustrated in figure (6), 28 points have been chosen and their co-ordinates have been 
measured in each quadrant. The image co-ordinates have been transformed from pixels to meter by multiplying each co- 
ordinate by the transformation factor. This factor is equal to 0.01056 which has been calculate from the distance 
between two points in the original orthoimage by pixel and its equivalent length by meter. The lengths between each 
point and the others (378 lengths) in each quadrant have been calculated. The lengths range is between .144 and 3.274 
meter. A comparison between the calculated lengths in the various quadrant has been done. This comparison shows that 
the average standard deviation of the lengths is .0353 meter. For purposes of the geometric comparison, two models 
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200 International Archives of Photogrammetry and Remote Sensing. Vol. XXXIII, Part B5. Amsterdam 2000. 
  
  
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