One of the following DTM Grid routines must be run in order for DTM contours to be generated.
These functions impose a regular grid over one or two terrain surfaces. Elevations are interpolated from the line data at each grid point and volumes are calculated. Particular attention should be paid to the general discussion on DTM Volumes.
The elevations on the grid generated by these routines are stored in a file with the same name as the terrain file, but with a ".grd" extension.
The calculations are only performed on the portion of the site that is currently visible on the screen. Therefore, if a volume of a particular area is required, the zoom functions should first be used to display the entire desired locality on the screen.
For volumes of terraces, it is quicker to use the dedicated Terrace Volume function.
It is always a good idea to contour the DTM grid in DTM Contours and/or generate a 3D View after creating a model. This should at least show up any gross errors that might exist due to one of the terrain points having an incorrect elevation.
You can create three types of DTM Grids:
Single Surface - Calculate a grid and volume from one surface to a datum.
Ground / Design Surface - Calculate a grid and quantities between two surfaces.
Ground / Design Difference - Calculate a grid and height difference between two surfaces.