Preserving hard edges on .obj export

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So this problem has had me chasing shadows for the past hour: I'm trying to export an .obj from houdini that preserves the vertex normals that I see in the viewport. I've tried using an attribute promote SOP for vertex N to point N, which doesn't work (it results in everything getting smoothed), and tried using a vertex SOP with cusp normal set (that just acts as a global smoothing angle, which isn't what I want). Searching around, some people say the attribute promote SOP works, some say that a custom .obj exporter is required (seriously?!)…

Can I export my model from Houdini, as .obj, to actually preserve my vertex normals, as I see them, in the viewport? There is almost nothing to go on in the documentation off of regarding this.

Thanks!
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Update: A fellow TD reached out and offered a solution: use a vertex SOP and set it to keep Normals before the ROP.

His explanation was:

by default I think it stores them in a different tabling than most obj exporters expect it, vertex should retable it

I'm not quite sure what's going on under the hood, but it did fix the problem; if anyone's willing to offer a more detailed explanation (since I don't see any difference in the attribute spreadsheet), I'd appreciate it. Thanks!
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Since Houdini 14 there is a new node called Normal which replaces the vertexSop in most cases, and should also solve this issue. Previously I would cusp with the vertex sop but since the normal sop I have been using that which seems t works as well.
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Problem with cusping is that it would blow out my custom vertex normals (this was modeled in another application). I merely wanted to use Houdini as an intermediate for doing some fancy stuff with the UVs and then export out for use in Mari.

I'll try the normal SOP method once I get back to work (I don't have HFX at home). Thanks! Could you explain what on earth is happening though? I didn't recall seeing anything change in the node attributes for the point attributes and the attr spreadsheet showed no changes either. I.e. is there another point attribute that I'm missing here that vertex/normal SOPs act on? What does the ‘tabling’ mean, if anything?
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