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Chapter 13: Modeling with Polygons and Patches

Delete Patch modifier
You can use the Delete Patch modifier to delete a patch subobject from a patch object. You use the Patch
Select modifier to select the patch subobjects to delete, and you apply the Delete Patch modifier to the
Patch Select modifier.
Using the Surface tools
The surface tools, which include the CrossSection and Surface modifiers, provide a way to model that is
similar to lofting. The CrossSection modifier takes several cross-section shapes and connects their vertices
with additional splines to create a spline framework. You can then use the Surface modifier to cover this
framework with a skin.

Cross-Ref
Lofting is accomplished with the Loft compound object. For more information on it, see Chapter 27, “Working
with Compound Objects.” n

CrossSection modifier
The CrossSection modifier and the Surface modifier are the key reason why the spline and patch modifiers
have been combined into a single submenu.
The CrossSection modifier works only on spline objects. This modifier connects the vertices of several
cross-sectional splines together with another spline that runs along their edges like a backbone. The various
cross-sectional splines can have different numbers of vertices. Parameters include different spline types such
as Linear, Smooth, Bézier, and Bézier Corner.
To apply this modifier, all the cross-section splines need to belong to the same Editable Spline object. You
can connect them using the Attach button. The cross-section splines are attached in the order they exist,
which can be a problem if you create them in a different order. The object to the left in Figure 13.45 shows
a spline network that has been created with the CrossSection modifier.

Note
Editable Splines include a CrossSection feature that works just like the CrossSection modifier. n

Surface modifier
The Surface modifier is the other part of the surface tools. It creates a surface from several combined
splines. It can use any spline network but works best with structures created with the CrossSection modi-
fier. The surface created with this modifier is a patch surface.
Parameters for this modifier include a Spline Threshold value and options to Flip Normals, Remove Interior
Patches, and Use Only Selected Segments. You also can specify the steps used to create the patch topology.
After the surface is created, you can apply the Edit Patch modifier to further edit and refine the patch surface.
In order for the surface to be created correctly, the vertices of the spline cage should be as close to coinci-
dent as possible. The Threshold value represents how close they have to be before they are considered
coincident. In addition, any closed loop in the spline cage can have no more than four vertices or a patch
will not be created.

Note
If the structure is already created, you can create a surface from the splines by simply applying the Edit Patch
modifier. n
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