Inverted normals appear in assembled surfaces
Article needs peer review
Solution
Summary
Surfaces that have been created by negative scale duplication, then used in the creation of assembled surfaces (MODEL-Create-Surf.Mesh-Assemble), will contain inverted normals. This can be irritating when trying to create, for example, a model of a head consisting of many surfaces, some of which have been duplicated in mirror fashion (e.g. the classic half head that is duplicated in a negative scale axis).
Solution
To circumvent this problem, follow this recipe (using as a basis a simple scene consisting of primitive surface grids):
- Place two Grids side by side, rotate both Grids in the 90o in the X axis, and freeze the active transforms for all three rotation axes (MCA-Transform-Freeze active Transforms cmd).
- Use Create-Surf.Mesh-Snap Boundary to snap the matching V boundaries of the two Grids together.
- Select the Grid surface with the Snap Boundary operator, and from the MCA panel hit the Freeze button to freeze the Snap Boundary operator.
- Duplicate the Grids in the negative Z axis (e.g. Z = -1).
- Translate the duplicate Grids in the Z axis, a few units from the original Grid (e.g. ?2.0 units).
- With the Duplicate Grids still selected, mark the MCA Scale XYZ transforms, and freeze the active transforms by executing the MCA-Transform-Freeze active Transforms cmd; you will notice that the duplicate grid's normals will invert in the same direction as the original Grids' normals.
- With the duplicate Grids still selected, run the MODEL-Modify-Surface-Invert normals cmd; the normals will point back in the opposite direction, as they should be.
- Finally, select all the Grids, and execute MODEL-Create-Surf.Mesh-Assemble to create the assembled surface.
Result: The surface normals of the Assembled surface will now all point in the proper (or same) direction, as originally intended.
Applies To: XSI 1.0,XSI 1.5 on NT,Win2K,Irix
Posted: 2/2/2001
