The situation is : Say you have a hi-res piece of geometry. You'd like to use a retopo'd low-res geo as a base mesh for subdivision and displacement. Mudbox doesn't really cut the mustard for this. And Maya's transfer map results are even more useless. Here's what you do.
- Bring in your low-res UV'd geo to Zbrush. Turn it into a polytool so it sits in Zbrush's memory.
- Now import your hi-res geo. It should replace everything in the scene
- Go to the Subtool menu, select append and look for the polytool of the low-res geo you just created. Click it.
- Hide the hi-res geo for the time being.
- In the Geometry menu, hit subdivide a bunch of times, to get enough hi-res detail. You probably don't need to go as high as the unoptimised hi-res geo.
- Go back to the Subtool menu, show the hi-res geo again.
- Click on the now-subdivided low-res geo and hit Project All. This is at the bottom of the Subtool menu.
- Now your subdivided low-res geo should have taken on the detail from your hi-res geo.
- Lower the subdivision level in the Geometry menu. Do the Project All again. Repeat for every lower level.
Now for the map generation bit
- Set your low-res geo subdivision level to it's lowest setting. OR to whichever level you want to use as your base in Maya/Houdini/whatever.
- In Z-Plugins, click Multimap Exporter and select the maps you'd like generating.
- Make sure Flip V is ticked ON.
- Make sure Smooth UVs is OFF.
- Subdiv level should be at 1 or whichever level you've chosen.
- For final map turn ON Adaptive.
- Turn on 32bit EXR.
- The rest is fine to leave as default. Scale should be 1.
- Click Export maps.
SHOULD WORK. DON'T HAVE MULTIPLE UV TILES. DON'T HAVE UV's ON THE EDGE OF A TILE. ZBRUSH IS STUPID AND WILL MESS UP YOUR BAKING.
