Hey all,
I was wondering if it is possible to retopologize in another app and then import that base mesh as the lowest sub level?? I did a search but didnt find anything. I have a feeling its not possible, but thought Id ask anyway.
Thanks.
_K
Yes you can. Export the lowest subd, retopologise then import back into your original mesh at the lowest division and you will replace the existing UVs with your new ones. You need to be careful that anything you do outside zbrush does not change you vertex point order or your mesh will explode.
Richard
You can also export a medium resolution version of you sculpture (something under 1M polygons–around levels 4 or 5) and and use that as a reference to build an entirely new topology in something like modo, silo, or topogun. (All these products have tools to help building topologies based on reference sculptures.)
You then reload your new topology into Zbrush and subdivide to an appropriate density. Then attach the original sculpture to new topology as a subtool, and use Project All (Subtool subpallet) to transfer the details from the original sculpture to the new topo.
-K
Okay thanks guys.
Sometimes I use Softimage, sometimes topogun for retopo. Moreover, new ZB will ask if you want to reproject the features to your new mesh…And it works pretty well. I suppose that’s the base of the whole GoZ
Topogun, hands-down.
Other options I have used include retopo in Modo (snapping) and Maya (live surface) with much success. But Topogun is just plain fast and easy, easy, easy to use. 
You may also want to look at 3D Coat. They have some really cool retopo tools, and they run on the mac too!