Microsoft Knowledge Base

• Softimage 3D for Windows NT, version 3.01
• Softimage 3D for IRIX, version 3.5

SUMMARY

It is possible to project and trim NURBS, and apply skin in Softimage 3D version 3.5.

MORE INFORMATION

To project, complete the following steps:

1. Create a NURBS object and the spline to project onto it. You may want to duplicate the spline, scaling it down slightly in order to speed up the projection process.

2. Select the NURBS object and Draw > Project on NURBS Surface.

3. Click on the largest of the two splines and select the desired projection method in the dialogue box.

4. Choose Preview to visualize your selection, then select OK. You can now deselect one of the curves to avoid generating useless projections.

5. Repeat steps 3 & 4 until all the curves you wish have been projected onto the NURBS surface. (You should use at least 4 curves.)

6. Hide the curves, leaving only the NURBS model with the projected

       curves visible.
   

7. Draw > Extract and click on the curves that have been projected onto the NURBS object.

8. In the dialogue box, click on each PROJ and click Extract.

9. This should result in a series of NURBS curves that are related to the NURBS object.

10. Turn on Show > EdgeFlags and verify that the edgeflags of all the extracted curves are in approximately the same place otherwise the resulting skin will be twisted.

1. At this point, you might want to use the largest curve to trim the NURBS object. To trim, select the NURBS object and Draw > Trim NURBS Surface, then click on the largest curve you used to project on the surface earlier.

1. Use the Surface > Skin function. Click on each spline in order of size, going from the largest one to the smallest.

2. Click with the right mouse button to create the skin.

3. Once the skin is created, you can modify it by modifying the curves you used to create it.

4. The skin should fit nicely onto the NURBS object, can be parented, etc.

Throughout the projection, trim and skin process you may opt to use relational modelling.

One of the benefits of using relational modelling is that you can modify the shape of resulting objects (such as skins) by modifying the original splines.

Also, using relational modelling will stop Softimage 3D from creating a cascade effect. For example, if modelling relations is not active when you project curves on an object, you will create a cascade effect whereby Softimage 3D creates a new object each time you project.

Another advantage of using relational modelling with this process is that, if the edgeflags of the extracted curves are not in the right place, you can rotate the original curves to remedy the problem.

Here are some problems to be aware of with the projection, trim and skin technique, and textures:

With this technique, you cannot distribute 2D textures equally over the two surfaces.

Your options are as follows:

• use a 3D texture, or
• use a mental ray shader.

REFERENCES

Softimage 3D Modelling User's Guide, p. 185-203. Softimage 3D Reference Guide: A to H, Interface, p. 317-328 and Softimage 3D Reference Guide: I to Z, Appendices, p. 1355-1359.

NOTE: Softimage Inc. is a wholly owned subsidiary of Microsoft Corporation.