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The concept of pooled minicomputer systems (Olsen, 1975) is under 
development by the Department of Defense with the collaboration of 
the U.S. Geological Survey. Special-purpose control computers on 
the existing analytical stereoplotters are being replaced by general- 
purpose minicomputers to provide flexibility for the addition of 
hardware and software modifications. Then the modified analytical 
plotters are interfaced to a central minicomputer in a distributive 
network, thereby increasing the versatility of the total photo- 
grammetric system. 
  
U.S. GEOLOGICAL SURVEY (TOPOGRAPHIC DIVISION, 1975) 
  
With the assistance of the Department of Defense, USGS has carried 
out a pilot project in digital photogrammetry--deriving digital map 
data from the AS-11B-1 stereomodel and generating graphics from the 
data. At the present time, USGS is converting its analytical plotters 
and related equipment to the .pooled minicomputer approach. 
  
  
A study was completed on the evaluation of density factors causing 
difficulties in automatic image correlation. The principal factors 
were determined to be: objects appearing in only one photo, large 
objects obstructing small objects, electrical noise, variations in 
scanning spot size. 
  
A Kern PG-2 stereoplotter has been modified to digitize planimetric 
data and terrain profiles for digital orthophoto systems. Additional 
stereoplotters will be digitized. 
  
  
digitally driven orthophoto system is under development to produce 
digital profile information from a stereoscopic model, store the 
information on magnetic tape, and control the off-line photographic 
unit that produces the orthophotograph. The system includes three 
subsystems: a profiling device attached to a stereoplotter, an 
electronic subsystem consisting of a profile-recording assembly and 
a playback or scanning assembly, and an orthophoto-output system 
consisting of a projector equipped with & three-axis servo system 
for off-line exposure of orthophotographs. 
  
The feasibility of enhancing the photographic quality of Landsat 
multispectral-sensor images by digitally processing and combining 
successive images of the same Farth scene is being investigated. If 
digital processing of Landsat images results in improved quality, the 
Scope of cartographic and other applications of Landsat could be expanded. 
The possibility of future developments that may provide an automatic 
system for small-scale mapping using Landsat materials is being investi- 
gated (Colvocoresses, 1974). 
  
  
FOREST SERVICI 
Investigations are in progress on developing procedures for construction 
of digital terrain models for solving a variety of problems. The system 
uses an XY digitizer, and photo-identified ground control to produce a 
digital terrain model. The computer produces a magnetic tape to control 
an XY output plotter. 
29.