In any case the planimetric and altimetric control points 
required for the photogrammetric mapping to be used for 
the final highway design will also be sufficient for the 
production of the orthophotos. Aerial triangulation with 
rigid adjustment procedures based on control points clearly 
determined by field measurements is recommended as this 
facilitates the homogeneous fitting of the neighbouring 
orthophotos (Ref. 5). 
Concerning the sheet lay-out of the photomaps used for 
highway work, it is best to combine two models in one 
map sheet. These models can be combined without any 
misclosures during the projection at the GZ 1. In this 
case no special retouching is necessary. For the map 
scale 1 : 1 000 it has to be considered that with an 
overlap of 60 % two models will cover one kilometer 
only with photo scales of 1 : 5 OOO or smaller. 
During the operational procedures at the orthoprojector 
  
GZ 1 the map corners can be set and exposed as well as 
other reference points of interest by a point- or cross- 
shaped diaphragm. Also the principal points of the 
alignment or other particular points can be flashed onto 
the orthophoto and used as well as control for the fit- 
ting of different overlays. For example, when fitting a 
cadastral map to the orthophotomap the flashing of con- 
trol points is useful. 
  
Of utmost importance for a good image quality are the 
photo-laboratory procedures. The diapositives for ortho- 
projection should be made by electronic dodging followed 
by a thorough check with a densitometer.