Polygons To Nurbs Coversion?

[DaJuice]

Hey folks, just a general question. Are there any apps that are able to convert non-mesh (n rows by n columns) geometry to NURBS? Is it possible?

[sibarrick]

I can't think of the names but there are tools/software for converting cyberscans to NURBs patches. Not sure how they do it though. The fine detail is then added back with a displacement shader.

[Jason]

I can't think of the names but there are tools/software for converting cyberscans to NURBs patches. Not sure how they do it though. The fine detail is then added back with a displacement shader.

17741[/snapback]

CySlice may be able to do it maybe? In the old days, we tried out Paraform. I'm not sure this still around though.

[thekenny]

Paraform is still out there. ... Karan can still hook you up. let me know if you want an address.

-k

[Andz]

Imageware from Unigraphics can do that. And also compare results from final surface to original point cloud or mesh vertices as you can see on the ilustration.

[DaJuice]

Thanks guys. I guess there is no easy one-click solution for this. No biggy, I was just playing around with the viewport vex shading and NURBS seems to work best with it. Speaking of that, it would be cool if SESI figured out a way to do hardware acceleration for the vex viewport stuff, because right now it's slow as molasses.

btw I noticed converting simple mesh geometry to NURBS in Houdini often won't work. For example:

lay down a default grid

extrude one side of the grid to add an extra row of polys

append a VEX Mountain SOP

and finally convert to a NURBS surface.

Instead of producing one continous surface it converts every individual primitive into its own NURBS patch. If you bypass the PolyExtrude it works as expected. Is there a trick or a secret to this?

[sibarrick]

Does the polyextrude convert it to polys? If so try converting it back to a mesh first before the nurbs convert, perhaps sling in a sort by vertex order first too.

[DaJuice]

Thanks Simon, tried that stuff. AFAIK the point order has no bearing on the conversion process. Nothing I've done with the Sort SOP has caused any changes. I'm pretty sure the Convert SOP is buggy, if you check out the attached hip you'll see what I mean.

wacky_Convert_SOP.zip

[sibarrick]

It is to do with the order. When you poly extrude all the new points are numbered consequentively starting at 100, this destroys the row column ordering. In the situations where it works notice how the numbering for the edge you have extruded doesn't break this condition.

I can't really see a way round this, the convert would have to do some pretty niffty analysis of your shape to determine that it could convert it to a mesh or NURBs surface successfully.

The only thing you can do is be careful what order you put into the poly extrude and only ever extrude edges where the numbering is continuous, ie doesn't skip from column to column. Or put another way only extrude rows not columns.

Here's an example file where each edge is extruded and converted, notice how I had to jump through some sorting hoops to get it to work.

wacky_Convert_SOP_si.zip

[DaJuice]

Thanks Simon, I checked out your file and I understand what you mean now.