Calculate fold angle between surfaces


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.

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

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) (13.7 KB) (22.3 KB)


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



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