I am currently working on a project where I have been supplied with a high poly obj to insert into a scene I have created. The model is over 18milliong polys which is way too high for the scene, so am looking to use ZBrush to reduce the polygon count, and export a normal map for the detail instead.
Could someone please explain the workflow for this?
As far as my knowledge goes I am going to need to unwrap and export the normal map before I reduce the polys. I have requested a ZPR file from the guy so I can access the lower poly versions, but he’s being incredibly slow.
You’re going to have to do a bit of prep work here. 18 million polygons is far too dense to effectively unwrap and UV.
The first thing you will need to do is duplicate the subtool so the original is preserved. Then you will want to use ZRemesher to create clean and evenly distributed, relatively low poly topology for the duplicate.
Mind, 18 Million polys may be too dense for a number of cpu intensive processes to work well on, so as an intermediate step, you may need to use Decimation Master to crunch the polycount down, in order for Zremesher to work better on it. Decimation does not produce topology of adequate quality for your needs, but it is a quick and dirty way to drastically reduce polycount while leaving detail mostly intact.
Now you should have your original high res subtool, and a low res subtool that will have lost most of the detail from the high rez subtool. In order to reclaim that detail, you will need to subdivide it adequately to receive the high rez detail, and follow the procedure for projecting detail from one subtool to another on this page.
You should now have a subtool with a low poly base of decently quality topology (though not animation quality), and multiple subdivision levels, with all the detail of your original mesh.
Unwrap the mesh at the lowest subdivision level, using UV Master or other.
Export your UV’d base level geometry, and apply the normal map to it in the target application. Your target application also probably has a number of things that need to be done correctly in order for the map to display properly, so expertise with that program will also be required.