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.