Model Carving System. 
The H. Dell Foster Company announced the Orthophotoscope RSS-900 at the Denver 
1970 ACSM-ASP meeting. Producing an orthographic negative of a projected stereoscopic 
model, it is intended as an extension of the capabilities of the H. Dell Foster RSS-300 
Stereoplotter. Features advertised include: 1) automatic exposure control, 2) 
supplementary optics for sharp focus in an enlarged optimum focus range, 3) exposure 
width adjustable from 0.05 to 0.50 inches, 4) facilities for loading and unloading 
photographic material under normal light level of work, and 5) automatic line dropping of 
contours. 
The device is to be compatible for future interface to the RSS-400 Graphic Quantizer. It 
is to automatically record on magnetic tape in computer compatible digital format, the 
X—Y-—Z positions at predetermined intervals. Further, by use of the RSS-4 DP Digital 
Planimeter, the areas of profiles are to be automatically computed and recorded during 
normal profile scan. Data provided from its recording on magnetic tape is to be compatible 
for off-line automatic plotting of profiles. 
One of the most significant photogrammetric instrumentation developments in North 
America in the last four years is the Gestalt Photo Mapper (GPM) (Fig 4) by Hobrough 
Limited, Vancouver, Canada. The gestalt (form, shape) approach, using a Ah matrix, 
differentiates this instrument from other orthoprinters. In essence, the GPM is an 
automated, computer-controlled, image correlation device which electronically produces 
orthophotos. 
The GPM is a relatively small analytic plotting instrument divided into four separate 
modules: 1) the scanning module for the diapositives; 2) the printing module which is 
located in a photographic darkroom; 3) the correlator module; and 4) the control module, 
a console containing a TV monitor, control electronics, a small computer, a teletype, and: 
steering controls for communicating with the computer. 
The GPM prints the orthophoto patch by patch rather than by the usual moving slit 
method. All transport systems come to rest before the printing of each patch, completely 
eliminating any dynamic errors. After exposure, the computer directs the printer to move 
the film, and the scanner to move the diapositives, on to the next patch and the process is 
repeated until the orthophotograph is complete. 
The gestalt approach permits the GPM to operate several times faster than any other 
orthophoto system. An additional feature, which simultaneously produces contours of the 
area photographed, is being perfected. Rather than sell its equipment, Hobrough Ltd. 
prefers to sell its orthophoto products. 
The GPM was unveiled by Mr. G. Hobrough [14] in a paper, “Image Correlator Speed 
Limits," which he presented at the ISP Symposium of Commission II, Munich, Federal 
Republic of Germany. A subsequent paper was presented by Mr. T. B. Hobrough [15] at 
the September 1971 San Francisco meeting of the American Society of Photogrammetry. 
Another new concept in Orthophotography was introduced by the Kelsh Instrument 
Division of Danko Arlington, Inc., during the October 1971 International Conference on 
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