User-defined UV mapping

You can map UV texture coordinates by specifying user-defined planes for UV projection using the Load Projection option within the Automatic Mapping feature.

The Load Projection option uses a polygon object that you specify from the current Maya scene. The object can form a cage around the object or be comprised of separate faces that intersect each other at its center. The Automatic Mapping projection manipulator updates when a user-defined object is specified for projection.

Criteria for user-defined projection objects

The object used as a user-defined projection object must have UV texture coordinates.
It is recommended that the projection object be comprised of separated polygon faces. That is, a polygon primitive that gets used as a projection object should first be separated into separate meshes using Mesh > Extract. (NURBS and subdivision surfaces are not valid surface types for use with Load Projection.)

In addition, it is useful to know that:

The UVs of the projection object determine the shape and location of the final projection mapping that occurs.
You can translate any face from the Load Projection object along its normal with no affect on the resulting projection.
Scaling or rotating any face from the Load Projection object will affect the resulting orientation and scale of the final UV projection. The projection manipulator updates when this occurs.
The maximum number of polygon faces that can be specified for a projection object is 31.

To load a user-defined polygon object for use with Automatic Mapping

Select a polygon object in the scene view that you want to project UVs onto.
Select Edit UVs > UV Texture Editor to open the UV Texture Editor.
The existing UVs for the object appear in the UV Texture Editor’s 2D view.
From the Polygons menu set, select Create UVs > Automatic Mapping> .
The Polygon Automatic Mapping Options window appears.
In the Polygon Automatic Mapping Options window, turn on the Load Projection option, then do one of the following:
- Specify the object in your current scene you want to have loaded as the projection object by typing its name in the Projection Object box.
- Select the object in your current scene that you want to have loaded as the projection object, and then click Load Selected. The name of the object appears in the Projection Object box. See Criteria for user-defined projection objects above.
Click Project or Apply to execute the Automatic Mapping feature.
The automatic mapping projection manipulator appears centered about the object in the scene view with blue projection planes that correspond in orientation to the planes of the Load Projection object you specified. That is, if the Load Projection object has 8 planes in various angles of orientation, the projection manipulator displays similarly.

NoteIn some instances, the Load Projection object may cause the planes on the automatic mapping projection manipulator to appear unexpectedly offset or skewed from the object you’re projecting on. This UV offset is based on the original UVs for the Load Projection object and doesn’t affect the quality of the projection.
You can unitize the UVs for the Load Projection object prior to projection so its UVs reside in the 0 to 1 texture space. While this will make the projection manipulator appear more centered about the polygon object it may not provide the UV mapping results you were expecting as the UVs will be projected similar to having explicitly specified the Overlap feature.
Translate, rotate, or scale the manipulator as required to achieve the UV projections you require. The projected UVs appear in the UV Texture Editor. You can observe them update within the UV Texture Editor whenever the manipulator is moved within the scene view.