Difference planar-srf creation

Rhino
1

Hi all,
if it were possible to indicate which criterion the _PlanarSrf command uses?

I tried to replicate it, I used the first example on the left in the photo:

immagine
immagine1103×513 12.3 KB

but as you can see the result of my procedure, is different from the single command _PlanarSrf
Apparently, PlanarSrf is oriented according to different criteria than the C-plane

(It’s just a question out of curiosity, and Thanks for any clarification)

edit:
I am wrong if I assume that the plane used is the one of reference to the object?

2

It seems the longest linear segment is used for the orientation of the surface.

The example on the right is a degree 3 curve rebuilt with 50 control points.

image
image1891×1081 123 KB

1 Like
3

Hi @martinsiegrist,

Thanks for your reply:

I was also trying to understand how it works with shapes similar to yours, and I noticed an interesting thing for me that I had missed, the orientation of the C plane with respect to the object which apparently, seems to be identical to the orientation of the Gumball on the object (at least on flat 2D geometries) takes into account the starting point of a curve with its tangency. so in a closed curve, moving the junction point changes the orientation of the C plane on the object. so if my reasoning is correct, in your curve on the left of the photo, the starting point should be found, at the ends of the long straight line. particularly interesting case after the reconstruction of the same curve on the right of the photo, in this case it seems to take the C plane as a reference.

1 Like
4

immagine
immagine911×462 5.91 KB

It seems my hypothesis is wrong.

5

I’m just guessing here, but maybe a minimum bounding surface rectangle is used by PlanarSrf as underlying surface?

6

it could be a solution, so by rotating the curve the orientation of the Srf should remain identical.
I’ll try it. thanks for the suggestion :+1:

ps if so, it means that there is a nice algorithm behind it that calculates
which orientation to give to the plane to have an area smaller than Srf