Problem understanding "Point Deform"


I am currently trying to learn the basics of Grasshopper reading Arturo Tedeschi’s book Algorithm Aided Design and I am facing an issue when replicating the mesh showed on p.274 (no definition provided) with “Point Deform”.

Here above the desired mesh. I replaced the 4 corner points of a 3x3 triangulated mesh by their offsetted selves (“Replace Item” + “Constructed Mesh”).

Based on this answer by David Rutten, I deduced (maybe wrongly) that the same mesh could be built using “Point Deform”. However when I feed that component with the appropriate Motion vectors, Control points and Geometry, the original mesh doesn’t change and remains straight like an XY axis plane.

Could someone explain what I am missing ? (11.2 KB)

It’s working fine in R5. You didn’t internalize your surface param so I plugged in a PlaneSrf to replace it. If you hide the green group, the red group is producing an identical shape.

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Thank you for the prompt reply.

Interesting. Is there an explanation as to why this work with a PlaneSrf and not with a Srf ?

Unless you internalize your Srf param and re-post the file, I wouldn’t know. It’s not the param, but maybe there’s something weird about how you created that surface?

P.S. Part of the problem is most likely right here:


The assumption that there will always be at least 16 points in the resulting mesh, and that these specific index values will always get the corners. With List Item ‘W’ (Wrap) true, it can cause duplicate points, as I just managed to do with a kite-shaped surface.

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I just restarted Rhino / Grasshopper and it seems to work now… strange.

Thank you for your time anyway and apologies for the inconvenience.