Hi there. My issue is after retopologizing in maya and importing all parts at once as FBX into zbrush 2021 every subtool is offset (only remedy seems to be activating local sym, but i really want to find out why this happened). The odd thing is, i have the original high poly ztool thats its symmetry is normal and am able to insert/append from one another with no issues. What can be the problem?
There’s not enough information here about your import/export process to do more than make some guesses, but we can examine the moving parts and it may help you to figure out where it went wrong.
ZBrush auto-centers every mesh at the geometric center of the combined mesh upon import. This also applies to the tool that results when imported from an FBX file set to save ALL subtools. It records the values required to restore the mesh to its original position upon export in the Tool > Export menu. If you see values in that menu next to the X,Y, and Z offset sliders, it means Zbrush has offset your model in the worldspace by that much in order to center it.
The most likely reason to see offset in ZBrush is that the dimensions of the mesh are not actually symmetrical along a global axis (even if a mesh is symmetrical in itself) and it is moving the geometric center, forcing ZBrush to offset it. Understand that even if the mesh was actually off-center in the original file it is being imported from, because of the auto centering it would still appear centered in ZBrush, as long as the bounding box dimensions were symmetrical. The actual offset would still be apparent in the external application it is coming from.
When importing an FBX file containing multiple subtools, it’s not like saving a native tool file in and out of Zbrush. It’s creating a new tool, and all the subtools contribute to the bounding box dimensions. It centers all the tools based on the center of their combined dimensions. If the bounding box is longer on one side of an axis plane than the other, it pushes the geometric center towards that side and you’ll see offset. Local symmetry will still work if the individual subtools are in themselves symmetrical, but global symmetry will fail.
So this is to be expected when importing visibly asymmetrical models, but in the case of a model that is supposed to be symmetrical yet is off center in ZBrush, this is usually the result of one of your subtools not being as symmetrical as you think it is. It could also be caused by errant geometry like a stray point or polygon distorting the dimensions of the bounding box. Make certain to force perfect global symmetry with the Tool > Geometry > Modify Topology> Mirror and Weld feature, or equivalent in whatever application you’re importing from.
If you want to import a mesh that is symmetrical in itself but has asymmetrical subtools pushing the bounding box off center, import the main symmetrical mesh separately, then import the other subtools and append them them as subtools to the main as in the following video:
When you import a multi subtool FBX file you’re importing all the subtools at the same time, under a single set of import rules, to create a tool. If you import them as part of an asymmetrical tool, Zbrush forces the entire tool to geometric center in the ZBrush worldspace and records the value to move it back again on export.
Each active tool, however, has its own settings in the Tool > Export menu, and appended subtools are governed by these settings. Your original tool has no offset values specified, and so the subtools append without offset.
I don’t know if any of this actually applies to your issue, but it should at least help you understand what’s going on a little better.