Inside the Help section, they reference three types of break lines:
- Break Line - Breaks are used to designate linear features such as edges of pavement, ditch bottoms, ridges, etcetera where an abrupt change of slope occurs. Any longitudinal element may be defined as a break line. Triangles will not cross a break line in the terrain model.
- Soft Break Line - A soft break line is a break line, however, if it crosses a break line, it will not affect the triangulation and is ignored.
- Graphic Break Line - A break line is a soft break line that is not stored in the terrain model.
We obviously understand the Break Line element. The two new ones however are either not defined all that well or difficult to understand how implemented. Actually though, it may seem like the Edit Terrain Model - Swap Line command may be utilizing the Graphic Break Line feature type. It happens, but it's not really stored.
As for the Soft Break Line, it should be defined as - A soft break line is a break line, however, if it crosses a break line, it will create vertices at the point of crossing and re-project the element to those new vertices.
For example, with a line added as a soft break line crossing a break line:
I drew a line from a spot elevation to a point on the edge of a driveway crossing the other edge of the driveway. Yellow elevations show elevation of the line where it intersects with the triangles...green are those elevations of the actual surface at the same points.
After adding the soft break line, three vertices are added and the triangulation changes as such:
You will notice that the elevation doesn't match what existing was (green) or where I drew the yellow line in space, but where it extrapolated between the endpoints and the breakline interception (purple):
Sorry ahead of time for color discrepancies...gotta love JPG conversion/uploads to the site. You should get the idea though.
As for soft break lines added not in contact with an already existing break line:
After adding it as a soft break line:
As you can see, the line reacts as a normal break line. The triangulation goes to where I actually placed the line.