Graphics Programs Reference
In-Depth Information
opportunity presents itself. For example, if one feature line crosses over another
feature line in the same site, one of the feature lines will bend so the two share
the same elevation at the intersection point. The point where they intersect is
called a
split point
. In cases where this interaction needs to be prevented, you
can simply place each feature line in its own site. Figure 17.2 shows two crossing
feature lines in plan view (left) and 3D view (right). Because these two feature
lines are in the same site, a split point is created, causing the red feature line to
bend so that it can match the green feature line.
Split Point
Split Point
FiGuRE 17.2
Two crossing feature lines that occupy the same site
understanding Feature-line Geometry
Feature lines have two types of points that define their geometry:
PIs
and
elevation points
. A PI is represented by a square grip and can be modified in
all three dimensions. An elevation point is represented by a circle grip and has
more constrained editing behavior. Figure 17.3 shows both types of grips on
the same feature line. The elevation of an elevation point can be edited, but its
location in plan view must slide along the feature-line geometry determined
by the PIs. This constrained behavior is actually quite handy because you can
create many elevation points on a simple plan view shape such as a rectangle.
Elevation Point Grips (Circular)
PI Grips (Square)
FiGuRE 17.3
A plan view of PI and elevation-point grips on a feature line
