9.5.2

430 • CHAPTER 7
OBJECTS MENU • DEFORMERS • 431
In some rare cases the accumulative nature of these options can lead to the prevalence of some
checks over others, with the result that no perfect decision for the reduction can be made. This can
be observed in some special cases when the sliver check and/or the boundary check prevails over the
fold-over check and so the nal mesh shows some fold-overs. What happens is that the algorithm
reaches a point at which it has to decide either to generate a fold-over, to break the object boundary,
or to generate a sliver. So it takes the user-dened quality factor into account and calculates the
better decision. In such a case, in order to avoid the fold-over, a higher Mesh Quality Factor should
be used.
Speed rst
Generally, all checks will slow down the speed of simplication to a greater or lesser extent. This is
because, for every potential edge collapse, each check has to take into account the face areas, vector
angles, orthogonal plane distances etc. for every one of the neighboring polygons.
General advice
Here is some universal advice about the use of Polygon Reduction’s options:
 On an object with co-planar faces use Co-Planar Optimization. This will speed
up the simplication signicantly.
 On co-planar objects, if not using Co-Planar Optimization, enable Polygon
Quality Preservation. This will generate a really well distributed mesh and will
work more quickly than with the option disabled.
 Leave the Boundary Curve Preservation option enabled. It will leave the
boundaries of non-manifold objects alone and will not interfere at all when
the object is manifold.