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> Tutorial 2 - Effect of Search
Radius
TerrainCAD for AutoCAD - Terrain modeling plug-in for AutoCAD
In this tutorial we will study the effect of the search radius
parameter on the terrain mesh.
Step 1: Delete the terrain mesh created in
Tutorial 1. If you are
starting from scratch then carry out steps 1 to 5 in Tutorial 1.
Step 2: Select Create Terrain from the TerrainCAD submenu or type
TCCreateTerrain at the AutoCAD command prompt and press Enter. At the
AutoCAD command prompt select points, lines and polylines select all the
points and press Enter. Specify a search
radius of 50 and press Enter. A mesh is created as shown below.
Terrain mesh with holes
You will find that the terrain
mesh created has holes in it and is incomplete (see figure above). This
is because the search radius we specified is not large enough.
Step 3: Use AutoCAD's Undo command to undo the creation of the
terrain mesh. Carry out the 2 step again and this time set the search
radius to 70. The terrain mesh created this time does not have holes.
This brings about an interesting question. Why don't we always set the
search radius to a very large value (say 99999999) or zero (which is
equivalent to a very large number since the search radius parameter is
ignored for a value equal to zero)? The answer is we can't always do
that because this may result in a terrain mesh which contains unwanted
triangular faces. In fact the search radius parameter is prevents the
generation of these unwanted faces. Lets see what unwanted faces are by
an example.
Step 4: Delete the terrain mesh and create it again by following
the above steps using the TerrainCAD command with a search radius of
zero. A terrain mesh will be created containing 829 faces (see message
in the command window) as shown below. Zoom into the area marked in red.
The boundary points
(highlighted in red) are joined by unwanted needle shaped triangular
faces. This happens because the boundary points in this point set do not
describe a convex polygon. As a result the meshing algorithm treats all
points as possible mesh edges and creates faces where it can.
Now delete the terrain mesh
and create it again using a search radius of 70. This time the terrain
mesh contains 828 triangular faces (1 face lesser). The unwanted needle
shaped triangular faces are no longer present in the terrain mesh (see
figure below).
An intelligent use of the
search radius parameter can yield accurate terrain meshes.
Tutorial 3
- Create Mesh from Contours
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