Subsurface in c#

Hi all,

I am a beginner of c# and what I am trying to do is to subdivide a surface into an equal size. However, I found some issues:

I thought it would be easier to subdivide the surface if I normalize it (so the domain for the width and length is between 0 to 1), but it won't works at all. I just get null output. However, it works when I change to use the actual size of the surface but the subdivision becomes not equal. (see the image below).

could someone explain it to me why this happened??

Cheers!

Attachments:

subsurf_test_c#.gh, 11 KB

Replies to This Discussion

Permalink Reply by David Rutten on November 12, 2017 at 10:49am

The domains of a surface have nothing to do with the shape or divisions. You can always change the domain to anything you like without changing the surface in any measurable way, it's just that the parameters are mapped in a different way.

We (McNeel) prefer if the domain of a curve or surface is roughly the same as the physical size of the geometry. This makes certain algorithms that solve for zeroes work better. However if you create a curve with length 40 (and thus a domain from 0 to 40) and then proceed to scale it up a hundred times the domain will still be (0 to 40) whereas the length will now be 4000.

When you take equal sized steps through the domain of a nurbs objects, you will not take equal sized steps through world XYZ space. It is very unlikely that the parameterisation of a curve or surface is consistent. Typically parameters tend to get stretched near the extremes, where the shape has to reach for the final control-points.

If you want to divide the surface into equal sized chunks, you'll have to figure out equal division (for example by dividing the edge curve into equal length segments) and then projecting those points back onto the surface UV space to see what the actual splitting parameters must be.

Permalink Reply by David Rutten on November 12, 2017 at 10:59am

Does the attached make sense?

Attachments:

subsurf_test_d.gh, 20 KB

Permalink Reply by ZAQI FATHIS on November 12, 2017 at 5:05pm

Hi David,

thank you very much for your explanation and example! it is very clear to me now.

Cheers!

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