maps from radar imagery, A stereomodel formed from radar photographs was successfully con- 
toured at a scale of 1:300, 000 with a 100-foot contour interval. In the test reported, stereomodels 
were formed with "same-side'" photographs, that is, photographs obtained from two flight lines 
on the same side of the terrain being recorded. However, the AS11A and supporting computer pro- 
grams will also handle "opposite-side'" radar imagery, in which the two photographs of a stereopair 
are taken from opposite sides of the terrain being recorded, 
Orthophotography 
While stereoplotters equipped with correlation systems have the capability of automati- 
cally producing contours and profiles, the problem of automatically extracting planimetric features 
from a stereomodel and reproducing them as line drawings has best been solved by using orthopho- 
graphs. Instruments for producing orthophotographs vary in sophistication from the simple 70-mm 
Hasselblad camera to the UNAMACE, 
Unscanned Orthophotographs - With the advent of high-resolution, ultra-high-altitude and 
space photography, it has been found that, within certain limits, rectified photographs can be used 
as orthophotographs of the earth's surface, Important limiting factors include flight height, control 
distribution, and terrain relief, DBA Systems, Inc., has developed a computer program for the 
USGS in which the project parameters can be entered as input in a simulation run, The image dis- 
placements at specified points are computed and printed as output, Thus, it can be determined 
whether or not the photographs of a project need to be scanned in an Orthophotoscope to produce 
orthophotographs. 
  
Automatic Orthophoto System (USGS) - An automatic orthophoto system has been designed 
by USGS to meet the steady and increasing demand for orthophotomaps and other orthophoto pro- 
ducts, The components of the system are the profiler, the Autoline, and the Orthophotomat, 
  
Investigations are underway to perfect an automatic technique for photographically re- 
cording terrain profiles in a model formed by a double-projection plotter. The profiles are formed 
optically by the intersection of corresponding rays projected from edge-enhanced positive and 
negative transparencies, They are recorded on film by simultaneously moving the projectors ver- 
tically and the film horizontally across the platen slit. Multiple profiles can be obtained simulta- 
neously. Further development is needed to improve the technique so that all profiles are recorded 
completely across the model, 
The prototype Autoline has been completed and tested, and the feasibility of the system 
has been demonstrated, This instrument follows profiles automatically by means of two photo- 
cells mounted side by side to straddle the line. As the Autoline traces the profiles, signals are 
generated to control the profiling motions of the Orthophotomat, Satisfactory orthonegatives were 
produced by the Autoline -Orthophotomat combination, 
The prototype Orthophotomat was completed and tested with the rest of the Automatic 
Orthophoto system, It is a single -projector differential rectifier for off-line, automatic produc - 
tion of orthophotographs, It scans and exposes the photoimagery in a narrow strip along the pro- 
file in the y direction and steps over automatically in the x direction to the next strip at the end 
of each scan, During scanning, z motion is controlled by electrical signals from the Autoline, 
The instrument consists of the main support structure, film platen, scanning assembly, and pro- 
jector assembly. The light-source assembly is mechanically independent of the projector, Inter- 
changeable exposing slots of different widths are available for scanning different types of 
terrain, 
Thematic Mapping 
The EROS (Earth Resources Observation Systems) program of the Department of the 
Interior is developing a thematic mapping system which is planned for installation at the new EROS 
Data Center at Sioux Falls, S.D., by mid-1972, This system is designed to accommodate a wide 
range of input data, but will initially concentrate on the mapping of four basic themes from photo- 
graphic data : 
- Open water 
- Snow and ice 
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