The UV coordinates of a texture projection at a location.
If you get this attribute on a spatial projection, the W value is dropped. If you set this attribute on a spatial projection, the W coordinate is set to 0.
If you get this attribute on a homogeneous (camera) projection, you get the raw, undivided UV values and the distance to the camera q is dropped. If you set this attribute on a homogeneous projection, q is set to 0 and stored in the W coordinate.
