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INSTRUMENTATION FOR INTEGRATED PHOTOGRAMMETRIC SYSTEM  U.S.A—7 
for photogeologic needs. These studies resulted in the development of the Ortho- 
photoscope, à device for converting conventional perspective photographs to 
the equivalent of orthographic photographs. The photographs produced with 
this instrument are practically free of displacements of images due to tilt or 
relief, so that horizontal distances can be measured accurately on them (See 
Figure 8). Such uniform-scale photographs have many important uses in map- 
ping, engineering, geology, forestry, and other scientific and military fields. The 
PERSPECTIVE PHOTOGRAPH | ORTHOGRAPHIC PHOTOGRAPH 
Scale = + , for objects Scale -- Uniform 
in datum plane only Image displacements -- None 
2 Perspective center 
Image displacements for reduction of 
Point A-* ag! orthographic 
Point B -- bb 
//\\ Projection to 
Negative = Projection plane Uniform - scale / ©  \Sny desired scale 
Ge positive 7 
/6 d ¢ ON 
    
  
  
  
    
  
f 
Lens =\/" Perspective _ + 
/ center 
Distorted - scale 
  
   
  
     
    
    
  
    
  
  
  
positive Hypothetical negative 
a =Projection plane n 
\ H 
Orthographic — “| 
Perspective X | 
projection rays projection rays 
| 
ig \ D. Ground 
AY ; |A | 
Datum plane IB Datum plane LI 
| | 
Ba B 
Figure8. Comparison of perspective and orthographic 
photographs, showing effect of relief. 
FrG. 8. Comparison of perspective and orthographic photographs, showing 
effect of relief. 
new instrument is operated in conjunction with an oriented model formed by 
any type of double-projection stereoscopic plotter using the anaglyphic princi- 
ple. A sensitized film is "scanned" by a slit in a screen on which the model is 
projected. The elevation of the film is varied according to the terrain as the 
scanning proceeds. The sensitized surface is film which is sensitive only to the 
blue light and not to the red light of the usual anaglyphic projection. When the 
scanning is complete, the film is developed as a negative and the "orthophoto- 
graphs" are printed from this negative in any quantity or scale. 
9. STEREOTEMPLETS 
Another U, S. Geological Survey development, although not strictly instru- 
mental, is stereotemplets, a new and highly effective means of radial triangula- 
ton of horizontal control. In this technique, the templets are obtained through 
the use of stereoscopic-plotting instruments. The basic data for these stereo- 
templets are derived stereoscopically from spatial models formed by the plot- 
ters, rather than from individual photographs. Because the model datum is ap- 
Proximately level and the photogrammetric control points are located ortho- 
graphically on the templet sheet, displacements due to tilt or relief are virtually 
eliminated, It is therefore only necessary to provide a means of adjusting the 
scale of the templet assembly. This is done by making two templets for each 
model and Using opposite corner points as centers of radiation, as shown in Fig- 
ure 9. The scale may be readily changed by shifting the templets along the azi-