Technical information

Creating Surface Data | 67
Key Concepts
■ When you import a point file into the Terrain Model Explorer, the point
data is not added to the point database. The data is used exclusively for
building the surface.
■ To add contour data to a surface, you must have contour objects or
polylines in the drawing.
■ To add breaklines, you must use the commands on the Breaklines shortcut
menu in the Terrain Model Explorer.
Creating Breaklines to Use in Surface Generation
Breaklines are constraint lines that represent abrupt changes in a surface,
such as retaining walls, stream banks, and curb; or breaklines represent
objects with known elevations, such as contours. You can use breaklines to
prevent surface triangulation across these objects.
Breaklines prevent TIN lines from crossing the breakline. This is essential if
the breakline represents a constant elevation, and you do not want eleva-
tions to be interpolated across such a breakline. The breakline also forces
retriangulation of the surface based on the breakline vertices.
The following illustration shows how a surface triangulates before and after
breaklines are created. When you define breaklines, you can control triangu-
lation with regard to abrupt changes in the terrain.