Ruben Posted May 13, 2005 Share Posted May 13, 2005 I`m importing OBJ geometry saved from Maya(with default options) to Houdini (with File SOP) and i get inverted normals and it draws black in the viewport, so i have to ReverseSOP it to get normals looking outward and correct view in the viewport. Is it normal or maybe i`m doing something wrong? Quote Link to comment Share on other sites More sharing options...
stevenong Posted May 13, 2005 Share Posted May 13, 2005 Hi Ruben, It is normal & has to do with the polygon order that Maya writes or Houdini's way of reading .obj files. Cheers! steven Quote Link to comment Share on other sites More sharing options...
Ruben Posted May 13, 2005 Author Share Posted May 13, 2005 Thanks steven! I guess, i`ll write a little mel, which will invert normals on polys and then export them to objs from maya. Quote Link to comment Share on other sites More sharing options...
Jason Posted May 13, 2005 Share Posted May 13, 2005 Yeah Ruben, this is normal. Quote Link to comment Share on other sites More sharing options...
Dennis Sedov Posted July 12, 2006 Share Posted July 12, 2006 Now importing obj is pretty much easy - ->Reverse->Facet (in case if you need to get your hard edges) Now what is really weird that there are no UV's Does anyone know how to solve this problem? Quote Link to comment Share on other sites More sharing options...
old school Posted July 13, 2006 Share Posted July 13, 2006 Don't know about the uv's (they should just be there if using .obj) but as for the normals, I would blow them away with a Point SOP. If you recompute the normals after reversing the prims, they change slightly! I don't know how maya generates normals. I suspect they "cheat" their normals slightly to enhance variation of surface topology in the viewport to "enhance" the modelling experience. Just my guess. I don't trust Maya generated point Normals in Houdini.. Quote Link to comment Share on other sites More sharing options...
stu Posted July 13, 2006 Share Posted July 13, 2006 I don't trust Maya generated point Normals in Houdini.. You and me both. Quote Link to comment Share on other sites More sharing options...
Jason Posted July 13, 2006 Share Posted July 13, 2006 You and me both. Yeah, you have to export vertex normals from Maya and then use a VertexSplit SOP in Houdini on "N". Here you get the same cusping you have in Maya but end up changing the topology of the mesh to do it. This is because Houdini sadly doesn't support vertex Normals (which is a hard thing to do at this stage, understandably). This an issue if you're trying to "round-trip" geometry back to Maya and you'd like the topology to remain the same. It makes you have to be a lot more careful but its doable. I can't remember if the Maya OBJ exporter exports vertex normals or point normals.. I think point, right? We have our own BGEO exporter from Maya that does the right thing. Cheers, Jason PS. When I say Houdini doesn't support vertex Normals, I mean that it does carry them on geometry like it would any arbitrary vertex attributes but they don't have special significance in the same way that point normals do. The Facet SOP, Cusp SOP and so on don't pay heed to them or generate them. Quote Link to comment Share on other sites More sharing options...
Dennis Sedov Posted July 13, 2006 Share Posted July 13, 2006 Yeah, you have to export vertex normals from Maya and then use a VertexSplit SOP in Houdini on "N". Here you get the same cusping you have in Maya but end up changing the topology of the mesh to do it. How exactly you export vertex normals from Maya? Quote Link to comment Share on other sites More sharing options...
Jason Posted July 13, 2006 Share Posted July 13, 2006 How exactly you export vertex normals from Maya? Well, I'm not sure you can without a custom plugin to do it. Unfortunately I know this is the problem but I don't know how to solve it with the available tools. As I said, ours is a custom BGEO exporter. Sorry this only helpful as information and not as a solution. Just thinking out loud, I wonder if there is a way to export two OBjs from Maya, one as-is and the other with every face unshared. Then attempt to transfer the point normals from the unshared model to the vertex normals of the intact original one and then follow up with a VertexSplit SOP. I'm not sure if it'll work because Maya is notorious for reordering stuff in an unpredictable way but it's worth the 15-minute workout to find out. Quote Link to comment Share on other sites More sharing options...
hoknamahn Posted July 16, 2006 Share Posted July 16, 2006 Now what is really weird that there are no UV's Does anyone know how to solve this problem? Houdini (at least versions 5-8) doesn't import UVs from OBJ files so the good idea is to write your own MEL/MAXScript/whatever converter from your package to Houdini's GEO/BGEO format. Quote Link to comment Share on other sites More sharing options...
Jason Posted July 16, 2006 Share Posted July 16, 2006 Now what is really weird that there are no UV's Does anyone know how to solve this problem?Houdini (at least versions 5-8) doesn't import UVs from OBJ files so the good idea is to write your own MEL/MAXScript/whatever converter from your package to Houdini's GEO/BGEO format. Houdini's OBJ reader certainly DOES support importing UVs (as vertex attributes). You can try it yourself: if you save out an OBJ from Houdini with UVs and then loading it right back in, the UV's are intact . The problem must be from whichever package you're writing out from not writing them out correctly (or at all). Make sure you have the relevant export options checked in the other package. Cheers, Jason Quote Link to comment Share on other sites More sharing options...
hoknamahn Posted July 17, 2006 Share Posted July 17, 2006 Houdini's OBJ reader certainly DOES support importing UVs (as vertex attributes). You can try it yourself: if you save out an OBJ from Houdini with UVs and then loading it right back in, the UV's are intact . The problem must be from whichever package you're writing out from not writing them out correctly (or at all). Make sure you have the relevant export options checked in the other package.Cheers, Jason Hummm... Really, I tried to import OBJ in H8 and I see correct UVs but I'm ready to swear that earlier it did not work with both 3DSMax and Maya OBJ exporters I don't understand Are you sure that H5-7 and first H8 builds understand OBJs UVs too? But maybe I'm liar... Maybe that was problems with Max exporter only. Quote Link to comment Share on other sites More sharing options...
Jason Posted July 17, 2006 Share Posted July 17, 2006 But maybe I'm liar... Maybe that was problems with Max exporter only. Heh heh, yep - it has always worked fine. We still interchange with OBJ a lot since we have some of those other packages like Lightwave and ZBrush for which we haven't bothered with a BGEO exporter.. and I don't remember any time it didn't work for us. Quote Link to comment Share on other sites More sharing options...
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