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With the Trim op you can cut out parts of a spline surface, or uncut previously cut pieces. When a portion of the surface is trimmed, it is not actually removed from the surface; instead, that part is made invisible. This means that you can still modify the surface (modify the position of its points, for instance) that is not displayed in order to affect the part that is displayed.
The surface can be trimmed by specifying open or closed profiles as inside or outside regions. The profiles need not be contained within the domain (UV space) of the surface; they can also be nested.
Open profiles are treated as follows: if both ends of the profile are inside the surface, the ends are connected to one another; if the profile’s ends are outside the domain of the surface they are projected onto, that part of the surface appears to be cut away.
Use a Trim SOP to cut a hole in the projected surface.
Use a Bridge SOP to skin the profile curve to another profile curve.
Use a Profile SOP to extract the curve on surface or remap it’s position.
Selection Method: Winding Rule
The selection method employed for clarifying overlapping trim loops is the winding rule, which executes overlapping commands instead of having them cancel each other out.
The following results were obtained by using a Project SOP to project two NURBS circles onto a NURBS grid. Then two Trim SOPs were added, one after the other, to the Project SOP. The first Trim SOP was set to Keep Inside, while the second Trim SOP had its operation changed as indicated.
The illustrations show a Gouraud shaded view of the resulting geometry.
Subset of profiles to use as trim curves.
Lists the types of trimming operations available:
Remove the area of the surface enclosed by the curve.
Remove the area outside the curve.
Trim based on the natural orientation of the profiles, be they open or not. Counter-clockwise profiles keep their interior, generating a result similar to “Keep Inside”. Clockwise profiles discard their interior, similar to “Keep Outside”, and may require an explicit outer trim-loop if none present.
Undo the trimming operation associated with the trim curve and turn the trim curve into a plain profile curve. Use the Delete operation to remove the profile entirely; this also applies to explicitly built outer-trim loops, which are regular profiles.
If the trim loops are viewed as contours on a map, the altitude is the “sea level” which marks the transition from trim in to trim out. $ALTITTUDE is the local variable containing the surfaces current altitude.
Process profiles individually
Generate a trim region out of of each profile or treat the whole group as one.
Build outer-trim loop explicitly
Generate a trim loop around the surface boundary. One is created automatically when a surface is trimmed for the first time if “Keep Outside” is on.
How close two trim curves must be to each other or to the edge of the patch to be considered an intersection.
The new altitude for the surface.