Graphics Programs Reference
In-Depth Information
10.
Open Surface Properties again. On the Definition tab, uncheck the
box next to Add Breakline, as shown in Figure 4.9. Click OK, and then
click Rebuild The Surface.
FiGuRE 4.9
Unchecking the Add Breakline operation
for the surface
You have removed the effect of the breaklines temporarily. Notice
how the TIN lines cross back and forth over the swale and ridge lines,
creating a rough edge where there should be a sharp, well-defined edge.
11.
Save and close the drawing.
You can view the results of successfully completing this exercise by opening
Add Breaklines - Complete.dwg
.
This exercise shows you the importance of breaklines. Connecting a bunch of
points together with 3D triangular shapes does not necessarily generate an accu-
rate surface. In certain areas, the shapes themselves have to be manipulated so that
they align with terrain features in order to model their form accurately. Figure 4.10
compares the surface with and without breaklines in both 2D and 3D views.
Breakline Settings and options
The Add Breaklines dialog box has several options and values to choose from.
Here is a brief explanation of each:
ty p e
Of the five types listed here, only two are important to discuss at this
time: proximity and standard. Standard breaklines have two jobs. First, they
control the alignment of TIN lines, as discussed previously. Second, their vertices
are a source of additional point information in the drawing. As you might recall,
the only point group you added to the surface is Ground Shots, so you'll need the
points to come along with any breaklines you add. For this to work, the vertices
of the breaklines must be 3D and must be at the correct elevations.
Proximity breaklines have only one job, which is to control the alignment of TIN
lines. Therefore, proximity breaklines only need to be 2D, but they must have
points in their
proximity
so that they can “steal” their elevations. If you had
added all the survey points to your surface, then the survey figures could have
been added as proximity breaklines.
(Continues)
