12. 
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NORDISK ADB'S TERRAIN MODEL 
Short description 
Fig. 1 
In Nordisk ADB Terrain Model the terrain is described by terrain lines. 
A terrain line is defined as a line polygon arbitrarily varying in x, y and 
z (northing, easting and elevation) but everywhere being defined at ground 
level. 
As the difinition of lines to be measured is general, the system has a great 
flexibility. The definition lines used by other systems are special kinds of 
terrain lines. The contour line, for example, is a terrain line with constant 
elevation. The cross-section is a terrain line with constant direction. The 
terrain line for describing an element makes it possible to use the line most 
suitable for the description of a terrain. Attention is drawn to the so called 
"break line", the edte of a road, a ditch bottom, the top or foot of a 
slope, the top of a mountain, a pits upper and lower edge. 
In areas where the terrain has a less defined shape, the break line may be 
replaced by cross-sections. Here the surveyor is free to choose the direction of 
the control line according to the terrain and not to the planned project. In 
forests it may be easiest to measure cross-sections in form of a star of vectors 
beginning at the instrument station. Thereby, clearance of sight lines in forests