0 
21 
Black and white film is most common but colour film is used on 
occasion. Colour film is generally more expensive. From the geo- 
metrical point of view and for mapping purposes, bland and white 
film is quite satisfactory. However, if the photographic mate- 
rial is to be used also for geotechnical photo interpretation, 
colour film might be the best solution. 
3.2 Ground Survey 
Planimetric control for the evaluation of the aerial photographs 
are in most cases arranged as a traverse. This is convenient be- 
cause of the long and narrow form of a road project. The average 
sidelength in the traverse is about half of the baselength bet- 
ween adjacent photographs in the flight strip. Occasionally the 
traverse is completed with single polar measurements. 
The distance measurements are made by using electro-optical dis- 
tance measuring equipment. The development of such instruments 
has made it possible to establish planimetric control in a very 
efficient way which has been important for the use of photogram- 
metry in highway design. 
Today electro-optical tacheometers are indispensable tools for a 
lot of measurements within highway design and construction. Es- 
pecially as many new types of these instruments have digital 
read out, on-line operations like reduction to horizontal dis- 
tances, facilities for automatic recording of data etc. The same 
instruments can be used efficiently for both traverse measure- 
ments, setting out and measurement of cross-sections and digi- 
tal terrain models. The following electro-optical distance mea- 
suring instruments are disposed by the Road Administration today 
17 AGA Geodimeter mod 6 or 6B 
23 AGA Geodimeter 12 
2 AGA Geodimeter 700 
11 Wild Distomat DII1O 
3 Wild Distomat D13. 
Vertical control for the photogrammetric evaluation is established 
in a conventional way using levelling or trigonometric height 
measurement. The method used is dependent on topography and vege- 
cation. 
3.3 Aerial Triangulation 
  
Applying aerial triangulation technique to highway design means, 
in the first place, that the triangulation in general has to be 
performed in strips. Blocks of strips are not very common so the 
conditions for using aerial triangulation for highway design pur- 
poses are from accuracy point of view somewhat restricted. Deci- 
Sive factors for using aerial triangulation include accuracy re- 
quirements, the condition of the superior triangulation net, topo- 
graphy, vegetation, personnel and instrument costs. It is also 
necessary to consider an efficient use of electro-optical distance 
measuring equipment when comparing aerial triangulation with ter- 
restrial methods.