UV propagation to smoothed topologies

Following are guidelines for consistent, distortion-free propagation of UV coordinates from simple polygonal topologies to smoothed topologies. These guidelines are particularly relevant to polygonal constructions such as buildings, which may have significant proportional variations among faces, especially where maintaining corners is concerned. In the examples below, we see a polygonal cube on the left with planar UV mapping for each side that is reflected in the UV Texture Editor snapshot on the right:

Ideally, we would like to see the following UV propagation when this polygonal cube is smoothed in Maya:

Note that the texture distribution on the smoothed topology is consistent with that of the polygonal base, and free of distortions. This propagation was achieved with the following Polygon Smooth options:

There are two settings of particular note. The first is "Smooth UVs", which is toggled ON by default. This setting smooths the topology's UV coordinates in a manner consistent with the smoothing of the vertices. Here is what the texture distribution would look like if "Smooth UVs" were disabled:

Note in the image on the lower left how the unsmoothed UVs on are bunched up near the edges of the cube, which produces the texture stretching seen above. Contrast this with the image on the lower right, where the smoothed UVs are distributed more uniformly, consistent with the vertex smoothing:

Another important setting in the Polygon Smooth options is "Keep Map Borders". By default this is set to "Internal", which on topologies with proportional variations among faces can produce the following distortions:

Note how the "pinning" of the edges produces curved texture distortions in those regions of the object:

However, when "Keep Map Borders" is set to "None", we achieve a faithful propagation of texture coordinates from the polygonal base to the smoothed surface:

Compare the uniform texture propagation near the edges with the previous distortions:

And note the difference between the edge treatments in the UV Texture Editor snapshots:

back