Planar Surface in Rhino Doesn't Match My Curve Exactly

Hello everyone,
I’m experiencing an issue with the “PlanarSrf” command in Rhino. I’ve drawn a closed curve and used “PlanarSrf” to create a planar surface. However, the resulting surface doesn’t perfectly align with the curve, and I can see noticeable gaps between them.

Here’s what I’ve checked so far:

  1. The curve is closed and seems planar.
  2. I’ve set my absolute tolerance to 0.0001 units
  3. The curve is fairly complex, with smooth transitions and several control points. I’ve used “SimplifyCrv” and “Rebuild” to reduce complexity, but the issue persists.
    The mismatch is particularly problematic because I need the surface to follow the curve precisely for further modeling work.

Questions:

  • Why does “PlanarSrf” not perfectly match the curve?
  • Are there better ways to create an accurate planar surface from a curve, especially for complex or detailed curves?
  • Could this be a display issue rather than an actual geometric problem?

Any insights, tips, or alternative methods would be greatly appreciated. Thank you!


Might help to upload the file.

This is a display mesh issue, not with the planar surface itself…

https://wiki.mcneel.com/rhino/meshfaq
https://www.hydraulicdesign.net/meshes.htm

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This took me a long time to get this, that the math is perfect, but the visualization is not. Thanks for the link.

it makes sense, I think I found a solution in your reply!
Using the rebuild command with a high number of control points seems to provide the definition and accuracy I need. By increasing the number of points, the rebuilt curve closely follows the original geometry while ensuring it works better with commands like Planarsrf

Thank you.

This is not a good idea. Rebuilding a curve with many unnecessary control points will result in overly complex objects that will complicate things downstream. Simply adjust your display mesh settings to get a better display matching your curves. The WIKI article explains how.

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Uh just to reiterate, it seems you took the exact wrong lesson from the advice you were given. DON’T WRECK YOUR GEOMETRY TO “FIX” DISPLAY ISSUES!

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Thank you for pointing that out! You’re absolutely right,
overloading a curve with too many control points can lead to unnecessary complexity and downstream complications. I really appreciate the reminder about the display mesh settings; it was something I completely overlooked in this case.

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