The Relax Tool can be used to refine an existing UV map, much like how the smooth tool is used to soften and regularize a models surface.
Usage
Any geometry with a UV map can be relaxed. The only prerequisite is to make sure that the target UV map is selected and that only the polygons that should be relaxed are visible. The relax tool is found in the 'UVEdit' layout. Its best to work here anyways to the results of the relax can be viewed in real-time in the UV viewport. LMB+click the 'UV Relax' tool button to activate. To relax the UV map, LMB+click in the UV viewport and drag the cursor to increase/decrease the Iterations value. When the tool is active additional options for refining the UV map are found in the tools properties panel-
UV Relax--
Mode: Users can choose from various modes that control how the Relax tool acts upon the target UVs-
Spring- Generates a 2-D type of dynamics simulation that makes all the edges in the UV map act like 'springs' pulling on each other trying to find the greatest equilibrium between springs. This method doesn't deal with overlapping UV very well.
Conformal- Relaxes the mesh using the ABF++ algorithm to smooth out the UV map, same as used by the Unwrap Tool.
Adaptive- Adaptive will attempt to retain the original relative polygon size from the 3D mesh surface.
Angle Based- Uses the 'Least Square Conformal Map' algorithm to smooth out the UV map, same as used by the Unwrap Tool.
Iterations: This value determines the number of iterations for unchanged. Increasing the 'Iterations' will relax/smooth the geometry, the number of iteration necessary is largely dependent on the complexity of the target mesh.
Interactive: The interactive mode offers users an amazing way to edit a UV map using 'Pins'. When "interactive' is enabled, users can LMB+click over any vertex in the UV map, adding a blue square handle to it. When there are more than one handles in the map (and a sufficient number if 'Iterations') users can interactively drag around the UV map to reshape the layout, as if it were a sheet of rummer that twists and pulls between the users added Pins. Removing Pins is doe by Ctrl+LMB+clicking over an existing Pin. Users can add as many handles as necessary, but fewer handles usually provide the best results. Use the 'Save Constraints' checkbox if you wish MODO to remember which vertices were set as pins each time the tool is used.
Seal Holes: If the target mesh is not "water tight" (such as a head with open eye sockets) the Relax algorithm can sometimes have difficulty resolving these areas. The Seal Holes option will create a virtual polygon to close the holes and improve the unwrapping effect.
Lock Boundary: The 'Lock Boundary' option will lock the outer boundary edge of all UV islands and will only relax the inside areas of geometry; the outer edges act like pins constraining the connected edges.
Area Weight: When using the Adaptive relaxation mode, the 'Area Weight' option determines a percentage amount that the relaxed mesh will attempt to retain the initial area of the modified UV island.
Save Constraints: When using the 'Interactive' option to Pin vertices, the 'Save Constraints' option will save which verts had handles and keep them intact for the next time the tool is applied.
UV Symmetry: When starting with a symmetrical UV map (such as created by the Unwrap Symmetrize' function) enabling the 'UV Symmetry' option will retain the symmetrical properties of the map while relaxing.
