«16. 
8,000 stereomodels. They demonstrate that a vertical accuracy 
of approximately + 2 meters can be achieved in aerial triangu- 
lation with statoscope of long strips in a routine production 
with control only at the beginning and end of each strip. 
5. CONCLUSIONS AND RECOMMENDATIONS 
Recent developments in horizontal block adjustment permit 
a drastic reduction in the density of horizontal ground control. 
This achievement minimizes the importance of auxiliary instru- 
ments furnishing horizontal information, but highlights the need 
for airborne auxiliary data for determination of heights of 
exposure stations, as well as of the angular orientation elements 
of the aerial photographs at the moment of exposure. In order to 
achieve progress in vertical aerial triangulation comparable to 
that reached in horizontal aerial triangulation, extensive use 
must be made of airborne auxiliary instruments (4). 
The simplest, least expensive but very effective instrument, 
is the differential height indicator - statoscope. It is in- 
dependent of terrain and does not require a special operator in 
the aircraft. It permits ceriol triangulation of long strips 
(20 to 25 models) and reduces by 1/3 the vertical ground control. 
An aerial triangulation system employing statoscope for 
determination of differences in height of exposure stations 
and APR for establishing of elevations of ground points virtually 
eliminates surveys on the ground and yields results suitable for 
compilation of contours at 15 meter intervals. 
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