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a) automatic interpolation of contour lines 
b) volume determination by the surface method 
C) optimizing of earth work quantities 
Reference is made to Sima (35). 
In.France the DTM-system named "semis de points" has been in 
practical use in the Highway Design work since 1968. The DTM 
is based upon fitting a surface to the measured points using 
a second degree function. Reference concerning the theory of 
the system is made to Baussart (6) and Deligny (29). The "Semis 
de points" system is used in the final design stage and the 
practical annual production amounts to 1000 km as an average. 
In the first stages of the Highway Design the vertical align- 
ment is designed along a chosen horizontal alignment using com- 
puter programs for optimization. 
The calculation of the DTM-data is made by a IBM 360/10 or by 
a control Data 6600. The automatic plotting in the system is 
made by a Calcomp-plotter. 
The Design system includes the following steps. 
1. Calculation and plotting of the axis. 
2. Measurement of profiles orthogonal to the axis. 
3. "Interpolation of the terrain surface. 
4. Calculation and plotting of the longitudinal terrain profile. 
5. Calculation of earthwork quantities and plotting of cross- 
sections. 
6. Plotting of horizontal alignment and perspectives. 
One of the problems connected to the existing DTM:s has been 
the requirement on big computers for taking care of all the 
data involved in the system. Some of the existing DTM, there- 
fore, divides the procedure in two step. The first step is to 
interpolate a square grid from the measured data and the second 
step is to interpolate the wanted surface or single spots from 
this grid. There might be a risk of decreasing the quality by 
interpolating in two steps but this fact has not been reported. 
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