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Trim NURBS surfaces

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Create or edit profile (trim) curves

Houdini supports curves on surfaces (also known as trim curves and profile curves). Profile curves are 2D curves that exist in the parametric (UV) space of their parent surface. Houdini draws profile curves as dotted lines on the surface.

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Create a profile curve on a surface

Trim a NURBS surface with a profile curve

  1. Create one or more profile curves on the NURBS surface you want to trim.

  2. Select the surface you want to trim.

  3. In the viewer, use the tab menu to choose the Trim node.

  4. In the parameter editor, choose whether you want to trim inside or outside the areas defined by the profile curve(s).

Extract a profile curve to a 3D curve

  1. Add a Profile node and in the parameter editor click Extract.

  2. By default, the operator deletes the surface it extracts the curve from. Turn on Keep surface to prevent the operator from deleting the surface.

Transform a profile curve

  1. In the display options, turn on display of Profile Numbers.

  2. Note the number for the profile curve you want to delete. This will be in the form 2.0 (for profile curve 0 on surface 2).

  3. Add a Primitive node. In the parameter editor, turn on Do transformation and set the Source group to the x.y profile number of the profile curve you want to transform.

  4. Use the Translate, Rotate, and Scale parameters or the manipulator in the viewer to transform the profile curve.

Delete a profile curve

  1. In the display options or the toolbar on the right side of the viewer, turn on display of Profile Numbers.

  2. Note the number for the profile curve you want to delete. This will be in the form 2.0 (for profile curve 0 on primitive 2).

  3. Add a Delete node. In the parameter editor, turn on the Enable checkbox below Number.

  4. In the Pattern parameter, enter the x.y profile number of the profile curve you want to delete.

Notes

  • Houdini has polygonal, NURBS, and Bezier profile curves. Each profile curve type is very similar to its 3D equivalent. For example, a NURBS profile can be open or closed, clamped or un-clamped, rational or non-rational, with order between 2 and 11.

  • The entire profile or part of it can move outside the surface boundaries, and become clipped at the surface edge. A profile curve that is partially or completely clipped is still valid and can be moved back onto the surface. See the Profile and Primitive sops for ways to manipulate a profile.

  • You can check whether a node’s geometry has invisible profile curves by pressing on the node tile. The pop-up info window shows the number of visible and hidden profile curves in the geometry.

  • A profile can co-exist with 3D primitives in primitive groups. A resulting mixed group would specify its elements like this: 1 0.2 6 2.9-2.17 4.*.

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