PHOTOGRAM METRIC ENGINEERING 
2 
Professor Schwidefsky, in his paper, de 
fined five steps of automation arranged in 
order of increasing performance which may 
generally be described as computers, analog- 
to-digital and digital-to-analog converters, 
signal orienters, signal correlators, and finally 
form recognizers. Photogrammetric examples 
of the first step are the classical stereoplotters 
and the more recent analytical plotters, and 
of the second step, automatic coordinato- 
graphs. Equipment representing the third and 
fifth steps exist only as experimental models; 
but the fourth step is illustrated by several 
instruments to be discussed in this paper, the 
best known of which is the Stereomat. 
Servo-Driven Plotting Table 
An example of the judicious application of 
new techniques to familiar problems is illus 
trated in the paper of Professor C. Trom 
betti, Instituto Geografico Militare, Florence, 
entitled, “Drawing Tables Driven by Elec 
tronic Servos for Analogical Photogram 
metric Plotters.” In this development 
synchro-transmitters are used to transfer X- 
and T-movements from the plotter to 
synchro-receivers on the independently 
mounted plotting table. The plotting surface 
of this table, the 030M, is exceptionally large, 
being 200X150 square centimeters. In order 
to avoid loss of transmission accuracy, a 
double-speed synchro-transmission is em 
ployed. Preliminary results showed that posi 
tioning accuracy was well within allowable 
map error, a result which could not be 
achieved with any other type of servo sys 
tem. 
Differential Rectification 
Another area which has received much 
attention in recent times is the production of 
orthophotographs. In a line map it is difficult 
to present anywhere near the detail found 
in an aerial photograph. As a working 
plan many earth scientists find the rich detail 
of aerial photography of special advantage. 
When he begins to measure, however, he 
quickly finds the differential scale relations in 
tolerable. The first correction the photo- 
grammetrist can offer is to correct the scale 
errors produced by camera orientation. 
Rectification of this type, however, ina plane 
correction which will not remove the scale 
errors resulting from terrain relief. This latter 
correction requires some process of differential 
rectification. Methods of achieving differ 
ential rectification include zonal rectification, 
the division of the terrain into polyhedral 
surfaces, the French method of facets, the 
Soviet method of the reversed terrain model, 
and the combination of differential image 
rectification with stereoscopic plotting. 
The combination of differential rectifica 
tion directly with stereoscopic plotting pro 
vides a magnification change continuously 
controlled by the stereoplotter. The first 
suggestion of this approach came from Lac- 
mann in 1931; however, his proposal was not 
instrumented. As early as 1935 Gallus-Ferber 
provided a typical example of what can be ac 
complished by equipment of this type. More 
recently, production instruments have been 
developed in America under the name of 
Orthophotoscope and in the Soviet Union as 
the Slot-Rectifier FT-Shch 1. 
In equipment of this type the model is pro 
filed in parallel strips and the image from one 
of the stereopairs is exposed differentially 
through a slit. If the model is created in a 
double-projection instrument, scale correc 
tions are made by varying the projection 
distance according to the scale on the profile. 
(If an optical model, as such, does not exist, 
as in the stereometer-type instruments to be 
discussed later, then, scale and displacement 
are determined by a computer.) The stereo 
scopic profile method is employed in the Slot- 
Rectifier, the American Orthophotoscope, and 
in the Gigas-Zeiss Orthophotoscope. 
T-64 Orthophotoscope 
Significant changes made in the ortho 
photoscope developed by the U. S. Geological 
Survey have been summarized by Marvin B. 
Scher in a paper entitled, “New Develop 
ments in Orthophotography.” At the Ninth 
Congress the cylindrical drum I960 Ortho- 
photoscope was described. The new T-64, 
shown in Figure 1, employs an inclined plane 
as the film supporting platform. Critical 
mechanical adjustments required in the 
drum-type instrument dictated the return to 
the flat platform. However, for operator 
viewing, comfort and convenience the plat 
form is tilted toward the operator approxi 
mately 40 degrees from the horizontal plane. 
In extending the area of coverage provided 
by orthophotography, the U. S. Geological 
Survey has produced orthophotomosaics. 
Scaling and orientation of the individual 
orthophotographs are accomplished by stereo 
templet triangulation. Uniquely, the data re 
quired for the stereotemplets can be derived 
directly from the orthonegatives.