SCOTT WILSON KIRKPATRICK & PARTNERS 
CHARTERED ENGINEERS 
Report on TERRA 
J Williams, London 
Spot levels are taken at random in a first-order stereoplotting 
machine. It is convenient to take points along lines parallel 
to one axis of the machine but the spacing of the points and the 
lines can be at random. The density of points depends on the na 
ture of the terrain and the accuracy that is required in the cal 
culations, but 40 points per acre is typical. The programs con 
vert the plotting machine co-ordinates to ground co-ordinates 
and they will interpolate the levels along any specified section 
line. This enables cross-sections to be derived along any high 
way line, from which the volume of earthworks can be calculated. 
The system will plot cross-sections of the cuttings or embank 
ments superimposed on the ground section, in addition to plans 
of the highway, large-scale outlines of plans of structures, and 
contours over the zone of interest within which the highway is 
to be located.