Problem : Planes follow curve and tangent on cylindric surface

Hi everyone,

I am trying to create planes which follow curves (letter) draw on a cylindric surface. These planes have to be tangent to the surface.

A few planes are correctly positionned but other are perpendiculare to the surface and I don’t understand why…

Somebody can help me please ?

Thank you !


the reason: a line has infinite normals, same as curves, but curves usually have curvature and as such a principal direction. Plane calculation is unpredictable.
the solution: If you want the plane normal to the surface for a specific point on a curve, you just need

  • point at the curves parameter (t)
  • tangent at the curves parameter (t)
  • the closest surface/brep normal from the point

If you create the crossproduct of both vectors(surface normal and curve tangent) you will receive a 3rd vector. Creating a new plane -> origin=point, xAxis = tangent and yAxis = crossvector yields the tangent plane. Try for yourself.

Hope I could help.

Thank you for answering.

I tried to do like you told me but I have a problem again…

I send you also my work :

cylindre (4790356) RhinoAutosave.3dm (161.3 KB) (9.8 KB)

Thank you for your help

obtain the closest points on the surface and evaluate the surface at those (15.8 KB)

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You could use Adjust Plane. (15.2 KB)

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You forgot the cross product @TomTom mentioned:


ah that’s right, sorry, i missed the curve tangent part in my response!

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Awesome !! Thank you so much !!