Strange render artifacts - help needed
Frank__
Posts: 302
I usually export scene subsets from Studio as obj and import them into Carrara - mostly because of dynamic clothing.
The first pic shows strange artifacts (I had this happen on another dyn cloth model, too, never on other meshes). It seems like the mesh is broken and I don't know what is happening here.
Pic 2 is the mesh in assembly room edit mode: it seems okay (as it does in the modelling mode) but pic 3 shows the breaks in preview render. It is the same as in the final render; happens in C8 and C8.5; no displacement in the shaders; not connected to lighting; still persists after untriangulating polygons; smoothing makes the breaks softer, but they are still visibly there - after 3 hours of finding a clue I'm running out of ideas. Anyone?
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Addendum: it's not a render problem, because LuxRender shows the same artifacts. Could this be a normals problem? Are there any programs out there, which could fix the normals problem (that is: not switch position but make all normals point outside)?
Could be normals, could be bad/goofy/duplicate polygons (though it looks like they're tris, so that helps).
Isn't there a unify normals feature in the Carrara modeller? One of my big problems with the Carrara modeller is the lack of tools to identify and fix stuff like this. Pretty bad.
I'll check, but I'm sure there must be a unify normals thingy...
With Carrara 7.2 (interface may be a bit different in C8.5):
You can display Normals by enabling it in the Interactive Renderer (little circle icon with an up-arrow) in the Vertex modeler and the Assembly Room view. You will need to set the option in each room if you want to see them in both. BTW, the option is at the bottom of the Interactive Renderer window.
If the Normals are mixed up, under the Model menu, there is a Reverse Polygon Normal command. Choosing this will reverse all the Normals so they are all going the same way. They will probably all be pointing inwards, so to fix that, choose the Reverse Polygon Normal option again. They should now all be pointing outwards.
There's no button that says "Fix ab-normals" ?
Get it?
Ab-normals ?
Oh, and you mentioned you tried un-triangulating polygons? Usually that does more bad than good. It can give you some really bad polygons if you're not careful. The algorithms in modelling apps for un-triangulating are historically pretty limited.
Triangles are generally pretty good in that it's impossible to make them non-planar, and non-planar can give nasty rendering errors, as well as other problems. So if you have them I wouldn't get rid of them.
Thanks, Joe and Evilproducer. I will check the "reverse normals"-command and see, if it helps, later, on my notebook.
Are you sure? It seems to me that this command reverse/flip all polygons, even if only one is selected. After applying the command I get mesh-breaks on other parts of the mesh, but they won't disappear. (Maybe I'm too stupid to apply the command correctly.)
I found somewhere on the internet that Blender can re-arrange all normals (in edit-mode ctrl+n), so I installed Blender, exported the mesh from Carrara, got some more grey hairs figuring out how to do the simplest thing in Blender, imported the mesh back into Carrara and voila: the mesh is fixed.
There is a bigger problem going on: after saving the file and then opening the mesh is broken again! :(
Did you freeze the dynamics in DAZ studio before exporting?
Also adding a smoothing modifier in DAZ may help, I add it even for animated dynamics when before clicking freeze, not so much running sim.
I also save as a duf scene and import into C8.5
Yes and yes. All the time :)
The new problem now is that Carrara invert normals while saving and re-opening the scene-file. There's a bug in the way Carrara saves (or reads) obj-meshes internally in the car-file.
Are you sure? It seems to me that this command reverse/flip all polygons, even if only one is selected. After applying the command I get mesh-breaks on other parts of the mesh, but they won't disappear. (Maybe I'm too stupid to apply the command correctly.)
I found somewhere on the internet that Blender can re-arrange all normals (in edit-mode ctrl+n), so I installed Blender, exported the mesh from Carrara, got some more grey hairs figuring out how to do the simplest thing in Blender, imported the mesh back into Carrara and voila: the mesh is fixed.
I did reverse all normals for the object by selecting just one polygon as a test, but rather than muddy the waters, and because it was late, I tried to keep my response relatively short and sweet.
From what I read, and from my limited experiment, reversing the normals and flipping them back had all the normals going the same way. I'm not sure what the issue is with your mesh.
Doing an experiment using a simple Carrara-generated mesh will work, but my experience has shown that finding an internal solution with something as complex as the OP has, with as many areas of flipped normals is pretty futile. You need a good mesh modifier such as MeshLab to fix that sort of problem.
Free, quick and easy:)
Yeah, like I said, Carrara really isn't the place to do any significant mesh analysis and repair. But it sounds like that's what you need.
Also, don't dis-count the possibility that it's something other than normals that are giving you the problem. I'm kinda surprised that you're saying Carrara has a problem when importing an OBJ like that.
That ripped look is typical of flipped normals, where the torn looking parts are the interface between good and bad normals.
Of course, it could be something else, but whatever it is, MeshLab can fix. Meshlab is pretty technical and you need to have a good understanding of topology - it doesn't have a "what is wrong with this?" button:)
If you have Hexagon, you can fix normals in a flash by using the unify normals tool.
Another very simple fix, if it is a normals problem, is to get the free Anim8or. When you select the model in face mode, good normals show yellow and bad normals blue. You can flip the bad normals individually or as a group selection.
Sorry, I got no email indicating I got another reply on my problem. Just stumbled over an open tab in my browser :)
It's a normals problem, because the aforementioned Blender import/export solves the problem.
It's not a problem importing the OBJ into Carrara. It's fine after the import. The problem occurs after saving the Scene-file as car and re-open the car-file (I do this sometimes to free memory or after a reboot :) ). Carraras internal handling of some OBJ-structures in its own file-format is broken; it's that simple. Broken.
My workaround is to keep the file open until I got my final render or import the OBJ again if I was forced to close Carrara for some reasons. Can live with this workaround, but it's kinda disappointing (and more) that Carrara has a bug in saving or reading a OBJ-mesh in its own file-format. C'est la vie.
Thanks for your help, but I got already the Blender-solution. Nice to know alternatives.