Graphics Programs Reference
In-Depth Information
Breakline Settings and options
(Continued)
Weeding Factors
Sometimes, the items you use for breaklines can have
too many vertices on them, and you'll want to eliminate some of them so that
your surface isn't overloaded with data. The selective removal of points based
on distance and angle is known as
weeding
.
Supplementing By Distance
Sometimes your breaklines will have long
stretches without any vertices in them. Because new TIN lines are created only
where there are points, and points are created only where there are vertices, some
supplemental vertices may be needed to improve the accuracy of the surface.
When you check the box next to Distance, Civil 3D creates more points along the
breakline that are spaced out according to the value you provide.
Supplementing By Mid-ordinate
Curves are a bit of a challenge because
TIN lines are straight and curves are, well, curved. For that reason, any curves in
a breakline are approximated with a series of short TIN lines. Just how short and
numerous these lines are depends on the mid-ordinate setting.
Mid-ordinate
is a
geometric term that refers to the perpendicular distance between an arc and its
chord. When this distance is short, the chord is also short, and multiple instances
of it can fit within the length of the arc. This might seem like a strange way to
define this behavior, but what's handy about it is that a single mid-ordinate
value works pretty well for a fairly wide range of curve radii. The following image
shows the effect of the mid-ordinate setting on a surface. The image on the left
uses a value of 0.1, and the image on the right uses a value of 1.0.
Editing Surfaces
With the inclusion of points and breaklines in the surface, you have essentially
provided all the data that will be needed to create the surface model. However,
you should continue manipulating this data until you achieve the most accurate
representation possible of the existing ground surface. You can edit surfaces in
Certification
Objective
