NurbsAddTrimCurve

From K-3D

Description

Adds a trimming curve to the selected patch

Plugin Status:	Experimental
Categories:	All Plugins, Experimental Plugins, NURBS Plugins

Metadata

Name	Value

Properties

Label	Description	Type	Script Name
Input Mesh	Input mesh	k3d::mesh*	input_mesh
Output Mesh	Output mesh	k3d::mesh*	output_mesh
Mesh Selection	Input Mesh Selection	k3d::selection::set	mesh_selection
Delete the Curve	Delete the curve which was used to create the trimming curve	k3d::bool_t	delete_curve
U Scale	Scale factor in the U direction	k3d::double_t	scale_u
V Scale	Scale factor in the V direction	k3d::double_t	scale-V
U Offset	U position offset on the surface	k3d::double_t	offset_u
V Offset	V position offset on the surface	k3d::double_t	offset_v

Description

Adding trim curves to NURBS patches is a difficult task, and hence this is the most difficult to understand NURBS plugin.

You should know that a NURBS patch is a surface spanned up by curves in u and v direction S(u,v). The range for u and v is the interval [0,1].
Trimming curves are closed curves defined within the parameter-space of u and v, cutting out a part of the parameter range.
By definition, while traversing the trim curve in its parameter range from 0 to 1 you discard everything to the right.

That said, when applying a NurbsAddTrimCurve modifier you need to specify a Patch and a Curve by entering their indices (you can find these by using GLNurbsCurveNumberingPainter and GLNurbsPatchNumberingPainter instead of their equivalents without the numbers).
The curve is used as trimming curve, but only its projection onto the XY-plane, so the z-component is discarded.
Then you have the possibility to scale and offset the trim curve(it is mapped to control vertices within [0,1]x[0,1]) so it maps into the parameter range you like, and you can flip the curve so it cuts out the other part of the surface.

Be aware that the first trimming curve you apply to the Patch always has to discard everything that's not inside the curve. So if you want to make a hole in your surface you need to add two trim curves. The first one including the whole parameter range, the other one cutting out a small part.