APPLICATION OF PHOTOGRAMMETRY IN ROAD LOCATION 
IN TROPICAL AREAS 
by B. Scherpbier. 
N.V. De Bataafsche Petroleum Maatschappij. 
Royal Dutch/Shell Group. 
Introduction. 
In locating highways in tropical regions which have already been developed 
to such an extent that large-scale topographical maps and an accurate geodetic 
base are available, photogrammetry can be applied in the same way as in Europe 
or the U.S.A., namely, by preparing maps to a scale of 1:2500, or even 1 : 1000, 
from aerial photographs, for which purpose a narrow strip is specially photo- 
graphed between the points to be connected by the road. 
With the help of the maps it is possible to make reliable quantity estimates. 
Use of aerial photographs in conjunction with maps affords a very good idea of 
the territory, with everything on it, so that all such natural and artificial features 
can be taken into account in planning the location of the road. 
There are, however, many tropical regions of which no large-scale maps exist, 
and regarding which the only detailed information available is in the form of sketch 
maps containing few data concerning elevation and natural drainage. In these 
areas, which are usually covered with dense jungle, photogrammetry can still be 
used with great success for the purpose of obtaining contour maps on which a 
preliminary road project can be made and which can also serve as a basis for an 
estimate of quantities of ground to be moved, dimensions of bridges and culverts, 
etc. 
Terrestrial Plotting. 
If a road has to be located in areas of which no aerial photographs are 
available, the only course open is to try to plot, on the available sketch maps, the 
connection between the beginning and the end of the proposed road via the 
governing points. 
In order to obtain a reliable project, a reconnaissance survey has to be carried 
out and a broad strip of the terrain must be studied. In the course of this recon- 
naissance a large amount of ground-surveying must, of course, be done, and, if time 
permits, it is even desirable to prepare a complete contour map of a strip between 
the starting and finishing points, via the governing points, with a width of 
between a quarter and a third of the length of the strip. Since, as a rule, no basic 
geodetic information is available regarding such areas, it goes without saying that 
this method of working involves considerable expenditure and time. 
Another mode of procedure is to make a preliminary reconnaissance survey 
throughout an area approximately as broad as that mentioned above, relying on 
field knowledge and planning sense, to obtain some alternative locations, which 
are later mapped in detail over a width of about 1 km. 
If the first method is applied one can be comparatively certain of ultimately 
finding the right location for the road. When the second method is applied there 
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