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variable: $ws -- tangential force shrink,sphere_morph,etc
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default: 0.5

The floating point parameter, $ws ("weight of
surface"), (F3 panel, lower left) controls the
strength of the tangential neighbor
redistribution 'force' in shrink() and
sphere_morph().

The tangential force is the resultant vector from
summing the vectors from the current vertex to
each of its neighors (and then subtracting out
the component parallel to the vertex normal).
This tangentially redistributes vertices so that
they are more evenly spaced.

Turning up $ws increases the 'stiffness' of the
surface and tends to make it preserve original
geometry better.

This alters the importance of original surface
geometry relative to the other 'forces' on the
vertex, which can include:

 shrink(), area_shrink(), shrink2d(), sphere_morph()
    $wn -- normal force
 area_shrink() and shrink_2d() only
    $wa -- perserve area
 sphere_morph() only
    $wcrv (0.5) -- curv targ img error weight
    $wsta (0.0) -- stat targ img error weight
    $wcpx (0.0) -- complex targ img error weight
 shrink_2d() only
    $wbn (0.5) -- boundary normal force
    $wsh (0.5) -- anti-shear force (quads only)

Of course, turning up geometry-preservation
implies that the errors minimized by the other
forces will be minimized less.  Registration
implies deformation :-}
