Help creating this simple shape without creases

I’m wondering if there is any way to create this object without the ugly creases as a NURB surface (leftmost object).

It is pretty easy to get a smooth object as a subD (middle object) , but I would like to find a clean and simple solution using nurb surfaces. I am a student brand new to NURBs techniques and am trying to rebuild some of my mesh models using surface modeling to learn more.

When I use the SubD to Nurbs command, the resulting object (rightmost object) seems to have excessive geometry. Would an elegant NURBs solution would use similar topology to the SubD? I actually cant figure out how to best manually model the middle shape as a polysurface with the corresponding rectangle and triangle faces. Or maybe the best solution to this has totally different topology?

Anyways… I’m wondering if anyone would help me figure out how to make this tube extrusion from a square base in a clean way :slight_smile:

Pipe_rect_Q.3dm (13.3 MB)

I think what you’re seeing may be render mesh artefacts. Check the page below for more information.

Thanks menno. Reading the link now. So you think this crease is just coming from the shader and doesn’t “exist in the actual object”? (not sure how to phrase this correctly, but I hope you know what I mean)

I can’t load the file to look at control point locations, but that is what I think yes.

Oh, is there something wrong with the file? I could try making another one and uploading.

I think the creases are actually really there though, check this out:

The file is fine, I don’t have Rhino on the computer I’ working on right now is all.

going from a square with 4 edges to a round(ish) curve is never optimal, let alone changing the surface direction by 90 degrees forcing it to warp inwards,

best you create a trimmed patch or surface on top, then blend surface or loft or whatever to the bottom like so, then you will get a good transition.