Trim NURBS Surface

The Draw->Trim NURBS Surface command allows you to trim a NURBS surface with a projected NURBS curve.

Trimming can be compared to using a cookie cutter: cut out what you want and use the different pieces that you create.

If you remove the trim region, the target object remains with a hole cut out of it. Alternatively, you may choose to crop or expand the trim region, in which case the solid "cookie" remains and all or part of the surface is cut away from it. You can combine the pieces in various ways; examples of which are shown starting.

Note:

By contrast, Draw->Project on NURBS Surface uses a similar method for projecting curves, but achieves a very different result. It allows you project curves onto surfaces without affecting the underlying surface at all.

For explanations of trimming works and detailed procedures, see the How Trimming Works section of the Modelling User's Guide.

Procedure

This is the basic process to follow. Detailed procedures are provided Procedure for Projecting or Trimming of the Modelling User's Guide.

1. Select a NURBS surface object.
2. Select a closed NURBS curve.
3. Position the curve in relation to the target surface; for example, translate it, scale it, or rotate it to the desired angle.
4. Select the target surface, choose Draw->Trim NURBS Surface and pick the source curve. The Trim NURBS Surface dialogue is displayed.
5. Accept the default settings or enter new ones for the following:

• The Projection Method and coordinate system you want to apply. You can verify the projection angle in the windows.
• Increase or decrease the Sampling data, if you like.
• The trimming Operation you want to apply.

6. You can always preview the results without trimming.

• When you click Preview, all the curves projected on the surface are listed in the Projected curves scroll box.
• You can click Ok to project and trim all of them, or select a specific one.

Tip:
The best way to verify your selection is to check which curve is currently highlighted in the window

7. You can delete trim curves using the Draw->Delete Trim Curves command.

Parameters

This is a description of parameters found only in the Trim NURBS Surface dialogue box. The remaining parameters, which are found also in the Project on NURBS Surface dialogue box, are described on Parameters.

Operation

A complete description of how trimming works and the procedures to follow is provided in How Trimming Works of the Modelling User's Guide.

Remove

Removes anything within the trim intersection area on the surface; this creates a hole in the surface.

Crop

Removes everything outside the trim region up to the next boundary encountered. This creates a boundary on the target surface.

Crop is intended primarily for use on areas of surface that fall inside the projected curve. When the projected curve intersects empty space, the Crop option has the same effect as Expand.

Expand

If the trim curve intersects with a hole in the target surface, Expand puts back everything within the intersection area, filling in the hole.

Where the trim curve intersects a solid (filled) area on the surface, Expand has no effect, since you cannot fill something which is already filled.

Last updated 08-apr-1998