Grasshopper

algorithmic modeling for Rhino

# How to change Planar Surface Trims And Best Fit Rectangles

I don't know if I can, but I want to get more control over the rectangular bounds used for planar surfaces.
In the photos below, you can see how some planar surfaces, when untrimmed are aligned to the world coordinate system, while others are aligned to to the edges of the regions used to make them. Is there a way that I can define the plane for each one?

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Also, What is the difference between "Copy Trim" and "Retrim"?

I'm waiting for the same answer as well...

With regard to the original question. If there is a Line-like curve it will align to this if there are more than one then the longest wins.

If proof was needed:

If that is consistently the case, then a work around for the original question would be

1. make a version of the planar surface trimming curves but with one long edge to align to.
2. make a planar surface with these new proxy trimming curves
3. untrim the proxy planar surface
4. project the original trimming curves onto the proxy surface (maybe this is where Retrim would be particularly appropriate?)
5. trim with new projected curve, for a new properly aligned surface with arbitrary trimming curves.

seems painful. Still wishing for a Plane input to Planar Surface (or has that already been done? I can barely keep up with David's constant interface improvements).

As a start, this is the way I would approach it.

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Sencond thoughts this would be a simpler approach to the identifying the keeper if, and this is the big if, the centroid of the original surface is inside your desired curve

That's a great solution for most similar cases, Danny, thank you.

Unfortunately in the situation when this arose (more than a year ago), the centroid would have often not fallen within the boundaries of the trimming curves.

Retrim takes the 3D trimming curves of one surface and projects them onto another surface. This will only work of the two surfaces are very close together and quite similar.

Copy Trim takes the trimming curves from the source surface UV space and moves them into the target surface UV space, this works on surfaces that are very different, but it's a UV mapping, not a 3D projection.

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David Rutten

david@mcneel.com

So retrim actually projects the 3d curves, and is not a UV-based remapping? How does it determine the projection?

"How does it determine the projection?"

Closest point. Retrim is not UV dependant. But it is very fragile, if the two surfaces are not close enough then it will fail.

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David Rutten

david@mcneel.com

Then retrim sounds like it should be the most appropriate solution for the original question. One could create a new planar surface oriented as desired, coplanar with the original, and large enough to encompass the original, and then use retrim to map the trim lines onto the new surface.

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