The operator can eliminate any local parallaxes 
during plotting, thus maintaining coincidence of 
the map and the stereo-model in the field of view. 
The APY instrument can obtain both the 
planimetric and height information needed for 
control purposes from the map which is set on the 
table. This method is convenient and there is no 
need for a knowledge of aerial triangulation or 
ground surveying. However, this method gives rather 
moderate results in terms of accuracy which may 
still be good enough for thematic mapping. It is 
important to realise that accurate height values 
are needed for the control points used for 
orientation, if high quality output is required. 
The heights interpolated from an existing map 
may be insufficient for this purpose. 
From the test results, it can be said that 
the planimetric accuracy of the APY instrument was 
  
  
  
  
  
better than its height accuracy. 
However , the planimetric accuracy of well- 
ntre defined detail is still within the Figure of 
of 0.3mm which is used by many national topographic 
to mapping agencies and therefore the orientation 
tna procedure using an existing graphical map for 
The control does satisfy the accuracy reguirements 
‚and for map revision. 
ints 
Ver, It has been demonstrated that it is possible to 
by incorporate into a low cost analytical instrument 
tes; the features necessary for a revision 
iar instrument. Attention should now be given to the 
Lion task of improving the existing systems and it is 
to be hoped that, in the near future, other 
manufacturers will enter this Field with 
new solutions, based on analytical principles, 
which are optimized for the revision of maps at a 
Qut variety of scales. 
arly 
Cane References 
: Tait, D.A., 1991. Instrumental requirements for 
ied modern map revision.Photogrammetric Record, 
cial 13(78) :901-908. 
at 
ions Turker, M., 1991. The revision of topographic maps 
ight using low cost analytical plotters. M.App.Sc. 
fo Thesis, University of Glasgow, 188 pages. 
nich Walker, A.S., 1984. A review of map revision by 
rors photogrammetry. Photogrammetric Record, 
Qu 11 (64) : 395-354. 
uals 
Ss Yzerman, H., 1987. The APY system for 
trol interpretation, compilation and revision of 
geographic data. Proceedings ISPRS/ASPRS 
International Symposium and Workshop on Analytical 
Qut Instrumentation: 347-354. 
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