=} 
114 CONVERGENT VERSUS VERTICAL PHOTOGRAPHY, SCHERMERHORN 
enhanced by the prior determination of these points, which will include the necessary 
passpoints. In that case it is only the precision of planimetry, apart from such consider- 
ations as coverage per model which will need to be considered. 
We will continue now with our listing of other viewpoints which are not based 
solely on the criterion of precision: 
4. Which is the resolving power over the whole model, with vertical and with convergent 
photography? 
5. Which angle, between homologous rays, is possible without considerably hampering an 
easy stereoscopic fusion and loss of precision of parallax measurement? 
6. Which is the consequence of the use of convergent photography for the choice of res- 
titution machines and for the cost of investment? 
7. Consideration must be given to any differences which there may be between vertical 
and convergent photography, in connection with the ease of the operations connected 
with both orientation procedures and with aerial triangulation. 
8. If there is a difference in capital cost of equipment, what is it and does it favour 
vertical or convergent photography? Is such a difference likely to be balanced by 
differences in productivity? 
9. Geometrical properties determine the coverage obtainable from a given flying height 
and several other important characteristics. 
Regarding geometrical properties, Dr. Brucklacher gave, as part of his contribution, 
the following information. 
He deals first with flat terrain. In accordance with the results of the 1.8.P./ 
O.E.E.P.E. experiments, it is justified to consider photographs at 1 : 12,000 on plates to 
deliver, in restitution, the same precision as photographs on film at 1: 10,000. The lon- 
gitudinal overlap is 60% in the verticals. The base length of the convergent photographs 
is such that the overlap between successive models is the same as for the vertical photo- 
graphy, although this would not be possible in the case of the usual American wide-angle 
convergent cameras with a convergency of 44.58. 
Brucklacher gives then the same values for large-scale mapping (film, 1 : 10,000) 
in mountainous terrain, where the height difference in a model is 420 m. The overlap in 
the convergent photography is such that the passpoint area is the same as in the vertical 
9" X 9" photography. Since the convergent system, in accordance with Netherlands ex- 
perience, is particularly suitable for mapping of strips for highway engineering purposes, 
Dr. Brucklacher gives in Table I data for a route 13 km in extent (scale of photography 
1:10,000, width of area to be plotted 1200 m). 
  
  
TABLE I. 
Number of Width of 
Camera ; 
models | strip 
RMK 21/18 (vertic.) 18 1440 m 
RMK 15/23 (vertic.) | 14 1840 m 
2 X RMK 21/18 | 
(convergency 308) | 10 1340 m 
  
  
  
Considering only the geometry of the photography, Brucklacher draws from his geo- 
metrical considerations the following conclusions based on photo scale 1 : 10,000 for film 
and 1:12,000 for glass negatives.