directly over the orthophoto. This enables the operator to observe the plotted (usually scribed) 
information together with the stereomodel and to check the completeness and the accuracy of his 
work. When the Stereocompiler is used for revision of maps a transparent copy of the map could 
be placed over the orthophoto. The operator then observes the map to be revised together with the 
stereomodel allowing him to plot any changes. The prototype Stereocompiler used for the map revi- 
sion tests at the IGN is shown in figure 1. 
  
  
  
Fig. 1 - NRC Stereocompiler 
An important feature of the Stereocompiler is its simplicity of operation. The only orien- 
tation procedure needed before measuring and plotting operations are undertaken is an alignment of 
the orthophoto and stereomate images. The instrument can therefore be operated to its full extent 
by someone without any significant experience in photogrammetric operations. The entire map revi- 
sion operation based on the use of stereo-orthophotos, including compiling the information from the 
stereo-orthophoto model, can be handled by cartographic technicians which may be beneficial for a 
smooth organization of this operation. 
References 
[1] T. J. Blachut : Mapping and photointerpretation system based on stereo-orthophotos. National Research Council, 
publication 12281, Ottawa, 1971. 
[2] T.J. Blachut : Methods and instruments for production and processing of orthophotos. Invited Paper, I. S. P. 
Congress, Ottawa, 1972. 
[3] T.J. Blachut, M. C. Van Wijk :3-D information from orthophotos. Photogrammetric Engineering, Vol. 36, 1970. 
[4] S. H. Collins : Stereoscopic orthophoto maps. The Canadian Surveyor, Vol. 22, 1968. 
[5] S. H. Collins : The ideal mechanical parallax for stereorthophotos. The Canadian Surveyor, Vol. 24, 1970. 
[6] R. B. Forrest, M. B. Alice : Stereorthophoto error analysis. ACSM-ASP Convention, St. Louis, Missouri, 1974. 
[7] F.Scarano, A.Jeric : Off-line Orthophoto Printer. ASP Convention, Orlando, Florida, 1973. 
DISCUSSION 
J. CRUSET - L'I.G.N., désirant acheter un nouveau jet, hésite entre le Mystère XX et le Lear Jet n° 35 ou 36. Ce der- 
nier possède une plateforme de navigation. Pensez-vous qu'on puisse adapter cette plateforme à l'utilisation d'une cham- 
bre à grande focale (F = 60 cm) qui donnerait une photographie où les différences de terrain auraient moins d'importance, 
ce qui éviterait toute restitution ou orthophotographie ? 
M. BACCHUS - La plateforme du Lear Jet n'étant destinée qu'à la navigation, il faudrait la transformer pour l'asservis- 
sement ; sur le Mystère XX, il faudrait en installer une, et nous pourrions librement en choisir les caractéristiques. 
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