Fig. 5. Map with different alternative road-lines. The result of the Balplex 
planning. Scale 1 :4000. 
planning direct in nature in the model, which gives a richer fund of in- 
formation than a map, however detailed, can ever give. However, 
through its anaglyph principle with the blue and red filters the instru- 
ment takes away some from the viewpoint of interpretation valuable 
detail information concerning the nature of the ground, especially those 
details which are judged in the light of their reproductions of colour- 
tones in the picture. In order that this information shall not be lost, 
the pictures are studied in the form of contact prints with the help of 
the mirror stereoscope in conjunction with the treatment in Balplex, a 
conjunction in which these two instrument complement each other ex- 
cellently. The mirror stereoscope is also a good aid in connection with 
the transition from e. g. the first three models to the next ones. It is 
then of course necessary to know what the projected roadline will be 
like in the sequel, and here it is possible to get preliminary information 
concerning the junction between the models by studying the succeeding 
pictures in the stereoscope. 
The construction of the instrument permits several people to work in 
it simultaneously, which is of value for the discussion as to the choice 
of route. 
As a result of the planning work a planimetric map with the different 
alternative road-lines marked in is shown. The map contains only those 
details which affect the road-line and which are needed to find it in the 
terrain. A suitable map-scale is 1:4000. Where a detail polygon system 
has been signalized for the photographing these points are also shown 
on the map. For every road-line a ground profile is also shown. In 
those sections in which the ground slopes sideways this is shown in the 
form of parallel profiles of cross-sections. 
8