6 
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III. Photogrammetric Satellite Triangulation 
The basic principles of photogrammetric satellite tri 
angulation are described in a paper which was prepared for 
Commission III for the previous Congress. Numerous pro 
fessional papers have since been published on the subject 
matter. 
By the time of the 1964 Congress, the U.S. Coast & 
Geodetic Survey had developed a system for photogrammetric 
satellite triangulation consisting of (1) data acquisition 
instrumentation and corresponding observational techniques, 
(2) a plate measuring procedure, (3) a numerical data reduction 
method and (4) supporting activities such as orbital pre 
diction procedures, timing service and general logistics. Pull 
scale tests had provided evidence in support of the feasibility 
of the chosen approach. Using the balloon satellites ECHO I 
and ECHO II, preliminary reductions from a number of missions 
had shown the average accuracy of a reduced direction between 
station and satellite to be about ±017. Detailed analysis 
of these results indicated the theoretical accuracy potential 
of the method to be ±01'4 to ±017. Expressed in terms of mean 
errors of the station coordinates, the studies indicated the 
possibility of determining the coordinates of the observation 
stations, by using redundant information, to one part in a 
million of the station to satellite distance. 
Thus, the conclusion was drawn that satellites in orbits 
comparable to those of ECHO I and ECHO II should allow the 
establishing of the points of a densification net in a con 
tinental area with an accuracy of at least ± 2 meters in all 
three coordinate directions. Stipulating as a goal a rela 
tive accuracy of two parts in a million between neighboring 
points, the average distance between stations can, therefore, 
be chosen to be about 1000 km. In the application of the 
method to the establishment of a worldwide net where, for 
geographic reasons, the average distance between stations 
is about 4500 km, the distances to the satellite are on the 
order of five to six million meters. Consequently, an accuracy 
of ± 6 meters should be obtainable. 
These considerations are reflected in the pattern of 
the world net, comprising some 40 stations, and currently in 
progress, as well as in the densification net of the North 
American continent area, established in part and scheduled 
to be completed at a later date. 
In Figure 1 the large triangles are part of the world 
net configuration and the smaller triangles form the densi 
fication net in North America, with solid lines connecting 
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