edge collapse
sphere error metric
greedy queue
discrete hierarchy
no border lock
patchsphere.small.ply
2nd LOD (19 tris) has a crack
(no apparent cracks when using big patchsphere.ply -- perhaps there's
 a problem with the input model that needs a larger tolerance
 sharing?)


half edge collapse
sphere error metric
greedy queue
discrete hierarchy
no border lock
patchsphere.small.ply (or probably any model)
segmentation fault when writing discrete hierarchy
(may have something to do with the new format for storing half edge
 collapse discrete hierarchies?)
