either the GZ-1 or Dell Foster RSS-900 orthophoto systems. 
A recent, unpublished report concludes that: 1) analytical aerotriangulation 
mensuration and orthophoto profile scanning have been tested and proven, and 2) 
independent model aerotriangulation, digitization of a stereomodel, and volume and area 
determination are all applications considered highly feasible. 
The United States Geological Survey reports the development of an Image Correlator 
and Measuring System (Fig 3). An automatic image correlator built for the U. S. Geological 
Survey by the BAI Corporation has been improved and is now ready for operational use. It 
scans an annular area of a photograph, or other form of imagery, and develops an analog 
signal, or signature, which uniquely describes the scanned scene. The signature is then 
converted to digital form and stored on a punched card. Subsequently, the reference 
signature can be reestablished from the punched card, and a corresponding scene from 
other imagery can be scanned and correlated with micrometer accuracy. 
A radial amplification module was added to the image correlator which permits the 
shape of the annular scan ring on the image dissector camera to be altered electronically. 
The ring diameter can now be varied to accommodate a considerable scale change. The 
scan ring can also be electronically stretched into an ellipse with the major axis in either x 
or y, and the annulus width can be held constant or differentially varied. This feature is 
expected to alleviate some of the scanning problems caused by anamorphic distortions in 
sloping terrain that are imaged from two or more widely separated perspective points. 
Some of the mechanical and electronic linkage for driving the monocomparator carriage is 
now being modified for easier pointing and positioning. 
Additional details, including summary test results, are given in Mr. Lorenz’ paper [1]. 
3. Differential Rectification 
One of the hallmarks of this reporting period is an increasing acceptance of the 
orthophoto as a valuable planning tool as well as a map substitute. The highly successful 
Orthophoto Workshop of January 1971, sponsored by the American Society of 
Photogrammetry and the American Congress on Surveying and Mapping, described uses in 
forest land management, regional planning, water resources investigations and land 
planning. Spurred by this wide user interest, manufacturers have improved existing 
instruments and have also introduced new systems. 
Items reported on here are: 1) a digital control unit for the Gigas-Zeiss Orthoprojector, 
2) the RSS 900 Orthophotoscope, 3) the Gestalt Photomapper, 4) the K-320 Orthoscan, 
and 5) the U. S. Geological Survey’s Automatic Orthophoto System. 
In November 1971, Concord Control, Inc., announced that they had recently installed a 
digital control unit on the Gigas-Zeiss Orthoprojector at the Engineer Topographic 
Laboratories, Fort Belvoir. This system controls the operation of the orthoprojector in 
accordance with information contained on magnetic tape, rather than the storage plates 
normally used in the LG-1 Scanning unit. These tapes can come from any compatible 
stereoplotter. They can be used directly in the production of digital contours. The same 
tapes can be used for producing 3-D models automatically on the Automated Terrain 
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