Heya,
Searched a bit on the forums but no luck. Ok, the issue im having is that when i take my hi rez sculpt which has polygroups, lower it to level 1 and export it out as an obj…then import into XSI and edit the points, then reimport back into Z with my tool active…the edits come through perfectly…which is AWESOME by the way…however, on reimport all my poly groups have disappeared. Is there a way to keep the polygroups intact? My second question is that when i have a hi rez mesh, like level 5 or so, and hide off say…the head…when i lower the torso down to level 1 and delete the hidden polys…the torso looses a ton of definition when i go back up to level 5. Is there a way to keep the definition or am i just running into some weird bug on this one particular mesh? Thanks!
For the first question…
The only way to keep the groups is to have each group defined by UVs in separate UV coordinate regions, and pressing the UVgroup button in the Tool palette upon re-import. But, then you have other things to worry about, like creating and rendering multiple displacement maps. I think you’ll end up wishing you had manually regrouped your polys…
The following thread focuses on the 3ds max/ZBrush pipeline, but you may find it useful in dealing with the above issue…read it in full
http://www.zbrushcentral.com/zbc/showthread.php?t=33127&page=1&pp=15
For the second question…
At your highest level, hide all but the torso (or whatever other body part you want to keep), under Tool palette > Geometry hit Delete Lower and Delete Hidden, 1) under Tool > Geometry hit the Reconstruct Subdiv Surface and 2)Move down to the new SubD Level, repeat 1) and 2) until you have the same number of SubD levels you had originally. This will allow you to retain all detail.
Hope that helps…good luck 
For the second question…
At your highest level, hide all but the torso (or whatever other body part you want to keep), under Tool palette > Geometry hit Delete Lower and Delete Hidden, 1) under Tool > Geometry hit the Reconstruct Subdiv Surface and 2)Move down to the new SubD Level, repeat 1) and 2) until you have the same number of SubD levels you had originally. This will allow you to retain all detail.
Smokebox : There is a better method to avoid the smoothing delete hidden causes. The one you desribe can cause problems if the original SubD level contains three sided polygons (they cannot be reconstructed).
A better and quicker delete hidden process:
- Hide model parts at SubD level 1.
- Go to the highest Subdivision level and mask all ( Ctrl + a )
- Go to subdivision level 1 and press Tool > Delete Hidden.
Thanks a TON guys!
Thanks for correcting me TVeyes 
I’ve never made any models with anything but all Quads, so I never have run into the problem you mentioned.
Thnx