Point at Parameter for a surface made of more than one loop?

Hi all,

I read existing threads on this topic, but this time I think it may be a limitation of the node “PointAtParameter”.

I understand the node works with the UV coordinates of the untrimmed surface, but the problem I am having is that if the surface is made of more than one loop, only the first loop is being processed by the node…

See screenshot, I get 2 surfaces from a subtraction node, then I union them together, but both noded and scripted “PtAtParameter” only finds UV coordinates for the first surface, not the entire, joined surface.

What you see in my screen shot is the blue (preview) surface with those circles cut out of it, however, a little sliver of surface is being separated from the rest of the surface, and that little first surface gets all the points of the “PtAtParameter” node…

The question is: how do I join the different surfaces so that “PointAtParameter” will spread the UV across all of them instead of using only the first one?

Secondary question is: is there another way scatter points on a surface (like grasshopper “populate 2D/ 3D”)?

thank you



Can you provide the source dyn or a similar graph to reproduce the issue? I am not sure that Surface.PointAtParameter is intended to work with polysurfaces (which is what you have here).

Also it helps to disable upstream geometry preview with issues like this, otherwise overlapping bits of geometry cause confusion.

I don’t think you can do this - the ASM supports untrimmed surfaces and is extremely limited whenever surfaces are involved. You would need to rebuild your surface to array points over two joined surfaces and this basic operation is nowhere to be found, not even in the Revit API, which is why you won’t be able to array points in the way you need, not unless you want to calculate a proportion of uvs across both surfaces but this is going to be useless if accuracy is important.

You should stick with Grasshopper and also look at Rhino Inside for tasks like this - free yourself from the shackles of Autodesks lacklustre geometry engines!

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