Converting trimmed surface to untrimmed surface

Is it possible to convert trimmed surface to untrimmed surface without changing its shape? (It seems that all untrimmed surfaces are shaped like rectangles.)

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If I can reconstruct the surface within a specific tolerance using the borders and perhaps some intersection lines (against perpendicular planes/surfaces) to capture the inner structure, I then recreate the surface using loft or Sweep2 or some other tools based on these curves. It all depends on allowed deviation from the original of course.

Fig 1. Sequence for recreating with NetworkSrf (in this case ended up within ~0.1 mm tolerance)

Fig 2. The final surface (to the far right) was then Rebuilt to the original degree, like so:

There might be better ways, but I always try using different Surface tools finding out what gives the best result (in terms of tolerance).

Flat surfaces are simple though, just detach the borders and use the edges to recreate the surface using _EdgeSrf and you’re done. Rebuild if you need to modify the degree and CP count, etc.

// Rolf


I was thinking about that couple of days ago. Alias and some other CAD programs have similar tool for converting a 4-sided trimmed surface into a non-trimmed one.

For four sided trimmed surfaces not trimmed on an isocurve, V7 WIP has testTrimRefit. Currently still a test command.



RIL, I like your technique for fitting a trimmed surface. I’m writing a script to create a surface grid for an aerodynamic panel code. Unfortunately, the UV domain that is returned to the script covers the whole underlying untrimmed surface, so that’s what gets gridded!

So what I do now is to take a number of isocurves in both directions, plus edge curves, from the trimmed surface and give them to NetworkSrf to create an equivalent untrimmed surface. It’s a lot of hand work, but it does work.