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Projecting a mesh from another tool

ZBrush Usage Questions
#1

So I exported an OBJ (a project of mine) that is giving me mysterious complaints of not being watertight. I loaded it into MS3d to utilize the auto-fix function, however the surface is now messy and not smooth or as detailed as it should be. I was wondering if i can somehow project the details and surface of the original file before it went through ms3d, to benefit from it now being recognized as a solid. I attempted to append the fixed mesh model into the project of the original following the zbrush-tips video for projecting. I cant seem to get it to work properly and was wondering if I am going abouts this correctly. Any details here for me?

I have already attempted to use zbrush’s built in fill holes, and mesh integrity test.

#2

Hello @ndsugi,

Is it ZBrush that is reporting the mesh isn’t watertight? This can be seen as part of the “Analyze Selected Subtool” report in the Transform Palette.

Without seeing the geometry I can’t tell you much. The problem could be as simple as a tiny hole in the mesh, or there could be sections of mesh that aren’t correctly welded causing it to be read as an open volume. Without knowing more about the situation closing the holes could produce problematic results.

We’ll get to projection in a moment, but here are some things to try with the original mesh:

  1. With your original mesh, make sure the entire mesh is visible and group it into a single polygroup with Polygroup> Group Visible. Now use the Tool> Geometry> Modify Topology Close Holes function. Any new polygons that are created for the mesh will be created as a different polygroup. Now use the visibility shortcuts to Shift-Ctrl click on the main mesh Polygroup which will hide all other polygroups. Shift-click on it again to hide that polygroup, making any other polygroups visible.

This should identify where the new polygons were created, allowing you to find the problem area. Press F, and then press F again to frame the new geometry in the viewport. If you see a few tiny polygons then there were simply some holes in the mesh. However if this operation produces large sections of geometry, then it is likely your mesh does not form a closed volume.

If the main polygroup does not hide no matter how many times you Shift-Ctrl click it, then there were no holes to close and no new polygons were created. The mesh is still a single polygroup.

  1. Use the Gizmo Deformer “Remesh By Union” on your mesh. This process will automatically close simple holes in the mesh and eliminate stray points that may be floating above the surface. The nice thing about this is that it will only alter the topology in places where this was necessary. If your problem is simple, this could be a very easy way to resolve it. If however your mesh is fundamentally unsound this could produce problem geometry.

Re: Projection.

Yes you can project the detail from your original mesh onto a new version of it, but I recommend doing the entire process in ZBrush. Just going through the standard process of converting a mesh into a multi resolution tool with a clean quad topology base and multiple levels of subdivision is likely to correct or identify the issue. This process will be required for the best results with projection in either case. No point in involving another program and complicating the situation with variables from that software as well as potential import/export issues.

For the best results when projecting you’ll want to retopologize your mesh, with ZRemesher or otherwise, into a closed watertight low poly mesh with clean quad topology. Note that ZRemesher will not close any holes or fuse any geometry. However if your current topology is too high res or haphazard, converting the form into a low poly quad mesh will probably make any issues much easier to find.

Then it’s a matter of subdividing that new topology sufficiently to hold the incoming detail, and projecting the detail from the original high res mesh onto the new one using one of the various methods.

Good luck!

1 Like
#3

thanks again friend! I never knew about the polygrouping + visibility trick, very handy.

What is the difference between remeshing by union and the other trick of appending a dummy subtool to create a boolean mesh, and hiding to delete the dummy afterwards?

#4

Remesh by Union works on the contents of a single subtool, while the normal Live Boolean process requires multiple subtools. This also means that unlike the normal Live Boolean process Remesh by Union is destructive. You can always just use this on a duplicate of the mesh.

#5

I think I understand. I was able to get the mesh to successfully read in zbrush as a solid via the 3d print hub plugin, however after creating a dummy insert, creating a boolean mesh, deleting the insert and re-scanning the mesh, it now renders as not a solid and the mesh integrity checker found many errors. Not sure why boolean meshing would change it to be less of a solid? I would just export the model pre-boolean meshing but I believe it’s better to have this as a solid when loading into my slicer software for printing.

edited

So I whenever i use the boolean mesh/remesh by union method to fix problem areas indicated in red, afterwards many new tiny nearly invisible problems are created keeping the model from being recognized as a solid. It’s driving me crazy! When I use the first method you suggested to see what the problem areas are, and split them into their own subtool, they are practically invisible. Should i bother trying to keep fixing these or just ignor them are send my project to print?

#6

Hi @ndsugi ,

I really can’t tell you anything about your mesh without getting at least a look at it. But its possible your mesh is problematic. Does it report issues with Tool> Geometry> Mesh Integrity> Check Mesh? If so you will need to deal with those issues. For simple problems “Fix Mesh” might work. But some meshes may have fundamentally problematic areas that will cause the mesh to keep developing these errors any time you do anything to it. In that case those areas will need to be identified and either redrawn in a topologically sound fashion, or cut away and resurfaced.

Dynamesh can produce highly problematic geometry if you try to use it on a mesh that has overly thin or 2D areas, or if you feed it a mesh that reads as an open volume rather than a closed solid. The mesh may begin to break apart in areas and that is going to be a problem for many processes. If your mesh has any sections of disintegrating geometry or fragments floating in space these will need to be cut away and resurfaced.

I would recommend going through the process I described earlier of converting the mesh to a multi-resolution tool with a clean low poly base, and try to build a better quality mesh. The results you get with ZRemesher will probably help you identify problem areas. It doesn’t fuse any geometry, so if you get odd results in an area you’ll want to look closely at these. Smooth the geometry with the smooth brush to move the points apart and look for issues with the topology.