5 
The data needed to bring the individual orthophotographic segments 
that make up the orthophotomosaic to the desired common scale and to 
place them in their correct positional relationship are obtained by 
stereotemplet triangulation. As the images on each orthonegative are, 
within the limits of the process, registered orthographically and at 
uniform scale, the information needed for the preparation of the stereo 
templets can be derived directly from the orthonegatives. This approach 
eliminates the need to reorient stereomodels to obtain data for aero- 
triangulation. 
The scanning operation is planned so that adjacent orthonegatives 
will have overlapping areas. After the common areas are superimposed, 
artificial pass points can be established by pricking through the ortho 
negatives. The artifical marks need not coincide with discrete images. 
Although the orthonegatives differ slightly in scale, this difference is 
insufficient to prevent the superimposition of images in a limited area 
containing the location of an intended pass point. Because many images 
are observed in the superimposed area, this procedure minimizes the 
detrimental effect of any local scan error in the vicinity of the pass 
point. When a significant reduction from the scale of the orthonegative 
to the final scale of the orthophotomosaic is necessary, a precision 
pantograph is used to transfer the pass point data from the orthonegative 
to the templet material. 
The positions of the pass points, as established by the stereo 
templet assembly, define make-line distances for use in the copy 
camera, in photographing the individual sections of the mosaic at the 
desired scale. The pass points, as recorded on the base sheet, furnish 
the information needed to position and orient each orthophotographic 
segment of the mosaic. 
Mapping Applications 
Orthophotographic materials have been used to great advantage by 
geologists and engineers to resolve problems resulting from inadequate 
map coverage in their areas of interest.3 How orthophotographs can be 
used most effectively in a mapping program remains a subject for study. 
Perhaps the geometric advantages of orthophotographs are not significant 
to the mapmaker because the stereoscopic model is available to him. How 
ever, other characteristics of orthophotographs are decidedly different 
from those of stereoscopic models formed in precise plotters. For example, 
an orthophotograph is a permanent record and can be reproduced on a variety 
of materials. It is re&dily portable and easily stored. 
Orthophotographs have been applied in map revision experiments to 
evaluate maps of doubtful horizontal accuracy and to determine whether 
the existing map is sufficiently reliable to serve as a base for adding 
new map data. Orthophotographs have also served as a source from which 
to extract new map data and as a guide to its positioning. 
The feasibility of compiling the planimetry of an urban area from 
a 1:24,000-scale orthophotomosaic was the objective of a recent research 
project. After various possible compilation materials and several printing 
techniques were investigated, a continuous-tone diazo rendition of the 
orthophotomosaic printed on a white, scribe-coated, scale-stable plastic 
was selected as most suitable for the purpose. The experiment established 
that the direct scribing of the planimetric information on this base is 
^Southard, R. B., 1958, Orthophotography--Its Techniques and Applica 
tions, Photogrammetric Engineering, Vol. XXIV, No. 3, p. 443-451.