Here’s a sample definition that allows you to perform draft angle analysis on meshes from inside Grasshopper. Should work in Rhino 6 and Rhino 7 on Windows (not Mac yet, sorry)

https://github.com/mcneel/ghgl/raw/master/src/tests/draftangle.gh

# Draft Angle Analysis Component

Dear Steve,

thank you so much. No need to go over bake/Rhino anymore (several times daily)!

Now one more little wish. It is really just a tiny step:

Please give a variable angle range (eg 0-1 Deg) white and the following range black color (here then 1-2 Deg) aso. Call the component isophotes analysis. Then we will have finally at true isophote highlight analysis from a fixed direction. Please also include this into Rhino itself to replace or complement the horrible Zebra light, which changes on geometry from every viewpoint. This will make a more professional touch. This isophote function is a longtime basic analysis in ICEMsurf, probably in Alias too. Its was also part of the VSR-Tools under Rhino5.

Best regards, Norbert.

Thank you very much.

You are definitely close to it. First condition is fulfilled: The pattern is not dependent on the view anymore but on a vector or plane. Excellent!

I am not sure if these are real isophotes. The screenshot shows a ball (left in isophote.gh, right in VSR-Tools). I will get back to you with a further analysis, but earliest sunday.

The further analysis on a sphere leads to the following conclusion: e.G. VSR-Tools divide the black/white stripes according to equally spaced section cuts normal to light direction. This is only valid to the sphere. Irregular shapes are not divided by section cuts but by isophote lines. I was not able to figure out what mathematical method was used to define the width of the black and white areas. It is **not** equally spaced angular ranges (e.g. 0-1 deg white, 1-2 deg black aso).