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SPATIAL AERIAL TRIANGULATION AT THE 
NATIONAL GEOGRAPHIC INSTITUTE 
by 
Ing. H. Bonneval (France). 
First communication: Operating method with machines. 
General principle: This is the method with “constant altitude” (B zero) as 
it has been exposed in a communication to the Congress in the Hague (1948). 
The operating method, however, has been remodelled substantially. One has 
tried: 
1. to reduce to a minimum the instrumental operating time, 
2. to utilize to a maximum the instrumental precision, preferring calculated 
corrections to the read elements above introducing corrections to the reading 
devices of the instrument. (e.g. scale-transfer), 
3. to reduce as much as possible the systematic and accidental errors. 
Goal, to furnish a network for the plotting on scales i : 40.000—1 : 100.000. 
Description of the operating method. The method, based on precedental 
considerations and applied for several years, has given great satisfaction and a 
good useful effect. 
1°). Use of photographs on glass only, application of wide-angle lenses. 
2°). Position of the photographs: the relative position of two successive photo- 
graphs in the instrument is chosen in that way that it corresponds at any time 
with a constant relative position of the two plates during the exposures. 
3°). Introduction of the plotting-cameras: once for all in the beginning of the 
mission, the operator changes the photographs without modifying the position 
of the camera. 
4°). Constant base: Bx as long as possible, By and B; are kept zero. Scaling of 
the models by calculation. 
5°). Double passage. All the traversings are executed two times, every model is 
formed successively with base outward and base inward. This has three 
advantages: 
a) No necessity to consider two different systematic errors; 
b) Reduction of accidental errors in the centering of the plates and in the form- 
ing of the stereoscopic models; 
c) Immediate elimination of blunders. 
Formation of the stereoscopic model: Improvements of the procedure 
exposed in the Hague: 
a) in quality: by keeping by — 0. The parameters are: X-tilt, Y-tilt and 
swing of the new photograph, Y-tilt and swing of the old photograph. The 
variations of Y-tilt and swing, given to the old camera are determined from 
readings on the reading-circles of the instrument. 
b) Useful effect: By suppressing (at least provisionally) the repetition of