Calculate fold angle between surfaces

Grasshopper
1

Hi

I have an error and I can’t work out what I’m doing wrong. I have two surfaces and I am trying to calculate the angle between them so that they can be folded for fabrication (sheet metal).

In Grasshopper I get the normals to the surface and calculate the angle. The reflex angle is 265 deg.

image1
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However, in Rhino when I measure it using Crease Angle Dimension and/or Angle Two Objects, it returns 275 deg.

image2
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I am assuming the discrepancy has something to do with the plane in which the angle is being calculated but I can’t work it out.

Any ideas?

error.3dm (47.8 KB)
error2.gh (13.7 KB)

2

Calculate_fold_angle_between_surfaces
Calculate_fold_angle_between_surfaces.png928×674 124 KB

error2_re.gh (22.3 KB)

3

Hi,

you measure not the crease angle but the plane-plane angle.
does the below explanation make sense?

image

-Willem

4

Are you suggesting the Rhino method is correct and the GH definition wrong?

5

Calculate_fold_angle_between_surfaces_re02
Calculate_fold_angle_between_surfaces_re02.png888×763 14.9 KB