Graphics Programs Reference
In-Depth Information
Components of a Surface
As shown in Figure 4.3, you can use many potential types of information to create
a surface and control its shape. The following list describes each one briefly:
Boundaries
Boundaries are used to control where the surface
is
. A boundary
around the edge of a surface can keep it contained within a certain area. Another
type of boundary can keep a surface out of an interior area, like a pond or building.
Breaklines
Breaklines force TIN lines to align with them. In this way, they
help to define hard edges such as edges of embankments, curb lines, ditch lines,
and so on.
Contours
Usually, we think of contours as the end product of building a
surface, but they can also be used as a source of data for a surface.
DEM Files
DEM
stands for
digital elevation model
, and it's typically associ-
ated with large-scale mapping that has relatively low accuracy. DEMs can often
be found alongside large-scale mapping data and are typically only accurate
enough for rough analysis or calculations.
Drawing objects
Drawing objects are AutoCAD
®
software entities such
as lines, blocks, and even text. These items can be used to help define a
surface as effectively as survey points, as long as they've been created at the
appropriate elevations.
Edits
Edits aren't actual data, but they do contribute to the makeup of a
surface. There are many ways in which a surface can be edited to improve its accu-
racy or usability. Some of these editing methods will be covered in this chapter.
Point Files
You've already learned that a point file is a text file containing
x
,
y
, and
z
data. So far, you've used these files to create Civil 3D points in the
drawing, but the same data can also be imported directly into a surface.
Point Groups
In Chapter 3, you learned that one of the benefits of point
groups is that they enable multiple points to be selected simultaneously. Using
one or more point groups to define a surface is one of the most important and
most common uses of point groups in Civil 3D.
Point Survey and Figure Survey Queries
These queries are created
using the survey functionality and utilize a sophisticated way of selecting points
and figures based on survey properties. These queries are not covered in this
topic but information about them is available within the Civil 3D help.
