### Grid subdibvision problem

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Hello,
I have been encountering this subdivision problem during the modelling process,i tried using edge loops but they won't solve the issue. What I also don't understand is why does it only happen on that particular corner?

Edited by FrancescoVerboso - April 15, 2018 12:26:00

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Sub.Prob.png (446.0 KB)

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I think it's just the way the algorithm interprets the geometry. I think if you add more geometry close to the inside of that corner, you should be able to retain something closer to a 90º angle.
>>Kays
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The green marked points are shared only by two edges, while the red one has more. The resulting approximation of any Sub-D algorithm is based on the angles between polys with shared edges. The green corners are single polys and therefore there's nothing to approximate.
This is not a Houdini thing, but a Sub-D thing. You'll get pretty much the same result in any 3d poly modeling program.
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Hi,

as additional info: if you want the corner become sharper, apply the crease node on all adjacent edges.

Attachments:
crease_subdivide_example.hipnc (72.2 KB)

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Thank you guys for all the answers,

@Midphase the main problem with adding geometry is that it will inevitably give me evident edges which i don't want and that i need to sweeten at the end with a polybevel. Also since I wil have to apply a car paint this edges will be very noticeabe.

@Aizatulin i tried with the crease after find iT out in Peter Quint's tut about subdivisions, and retried now after you suggested i, but donesn't seem to work for that edge unless i polyetrude first and also crease the lower edge. Unfortunately it gives very nasty topology

I also tried polybeveling the point and it kind of works, bu still very nasty geometry.
Edited by FrancescoVerboso - April 15, 2018 14:00:24
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Hi,

I've tried to rebuild your geometry roughly. For me it seems to work better, if you select only the both smaller edges.
Selecting the first “smaller” edge can be an option too, btw I haven't tried bolybevel.

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crease_subdivide_example_N.hipnc (88.7 KB)

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Hi Aizatulin,
it still doenst give me a clean result on the geometry unfortunaly, i managed to get this, polybeveling the point but still the shading has some artefacts given by the bending of the subd. How whould you approach the modeling of a door of a car, where the frame has to be a different piece disconnected from the windshield?

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Screenshot from 2018-04-16 19-16-26.png (252.9 KB)
Screenshot from 2018-04-16 19-14-51.png (398.3 KB)

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One does not model real-life objects as mere 2d surfaces. Closed volumes is the way to go. In some cases, you can get away with leaving a piece of geo as an open mesh, but identifying what are those cases is something modelers figure out as they accumulate experience.
Poly modeling aside, what you're trying to do there, is to seamlessly combine a flat surface with a curved one. Of course something has to give. There's no real-life car door that looks like what you're trying to model there. Unless it's a Renault or a Fiat.
So back to the initial idea - look for references and try to model exactly as they are, with thickness (no back-faces visible) and separate pieces.
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Hi inhiding,

thank you for your feedback. I wouldn't leave the door as a 2d surface, I would then exrude it to give the requested thickness and then polybevel the edges that I am interested in so to have more control after the subd. I might restart the piece directly with a box rather than a grid and see if i can achieve better results. Thank you!