the practical application of photogrammetry to highway design, 
as the combination of geodetic methods and photogrammetric e ^ 
triangulation can be organized in a more efficient way than be- 
fore for the horizontal and particularly and for the vertical 
control. 
The preliminary design stage can be divided into two phases. In 
the first phase one centerline is chosen from among the alterna- 
tive centerlines within the corridor. In the second phase the 
horizontal and vertical alianment of this centerline is fitted 
in, more in detail, to the surrounding terrain. This division 
into two phases facilitates the compromise between the require- 
ments on an overall view and geometrical accuracy. Therefore a 
rational design technique admits the use of the same photographs 
in the two phases. The evaluation principles are, however, diffe- 
rent. 
As in the first phase of the preliminary design different alter- 
native centerlines are evaluated within the terrain corridor, a e © 
great part of the detail mapping can be saved if the evaluation N 
is made directly in the photogrammetric model itself. The model 
itself contents generally more complete information concerning 
the terrain topography and geology than a map can afford. 
Consequently photogrammetric equipments as the Balplex Plotter 
can be used for the evaluation of the photographs in the first 
phase (see fig 2). This piece of equipment, provided with an 
auxiliary hydraulic lift, gives the designer not only an accep- 
table overall picture, covering wide areas, the entire model or 
a set of models, but also the geometrical and geological infor- 
mation concerning the terrain, that is needed for the choice be- 
tween alternative solutions. The geometrical information is shown 
on a planimetric map over the alternative centerlines at the 
scale of 1:2000 - 1:4000. The planimetric terrain details that 
are influenced by the centerlines or that have any influence upon ! ; 
them, are also shown on the map. Numerical height information 
for different alternatives is shown in the form of longitudinal e Q 
profiles and transverse profiles.