all measured points selected points 
  
Instrument at 1:10 000 | number | at 1:10 000 | number 
fp | mr | of MR my of 
mm mm points mm mm points 
  
  
  
Gestalt Photomapper I 0.036 | 0.017 
Gestalt Photomapper II | 0.028, 0.018 
  
497 0.036 | 0.021 115 
  
  
  
  
  
| 
7| 375 0.052, 0.018 86 
| 
  
TABLE V. Radial and tangential components of standard errors for 
all measured points and for selected points located 
within 1 mm (at the sale of the original photos 1:10 000) 
from elevated features 
While there is some deterioration of planimetric accuracy for 
these points, the results are still very good by general orthophoto 
accuracy standards. For the Gestalt Photo Mapper II the deterioration was 
smaller because this instrument can partly compensate for sudden changes 
of the correlation level. For the manually operated orthophoto instruments 
no significant difference was found between standard errors determined 
for the two groups of control points. 
The grid tests made on the Borrowdale cartographic camera indi- 
cated that, with proper care, a satisfactory accuracy can be maintained 
throughout the process of reducing and enlarging orthophoto transparen- 
cies. This was also supported by the Stereocompiler measurements of ortho- 
photos which were not submitted at the scale originally requested (see 
Table I) and their enlargements to the scale 1:2 500 which were made in the 
Borrowdale cartographic camera. No significant difference in the standard 
errors, between the orthophotos originally submitted and their 1:2 500 
enlargement was established. This indicates that the additional scaling 
of orthophotos that is required when the original orthophoto cannot be 
produced directly at the requested scale does not have to result in an 
appreciable deterioration of the orthophoto accuracy. 
Evaluation of Digital Height Information and Drop Lines 
  
There is no doubt that the accuracy of vertical terrain information 
- mostly profiles - used in orthophoto rectification processes depends, to a 
large degree, upon the skill and care of the operator. However, assuming 
that the participants made an effort to submit results of as good a quality 
as could be expected, the available experimental material could be