Inconsistency in "Evaluate Surface" component (GH 0.9.0069) ?

Dear GH developers,

It seems that the "Evaluate Surface" component in GH has an error or conflict with Rhino regarding the direction of the Normal of a surface.

I attached here a simple Rhino 5.0 model containing 6 surfaces (patches).

The function of the attached GH-script is to generate Normal lines at the centroids of the input surfaces from Rhino. The input surfaces have all the same direction, here "upwards" according to the "Dir" command in Rhino.

As a "normal" user, I was expecting that the generated Normal lines in GH have the same orientation/direction as their corresponding input surfaces. However, NOT all generated normals are equally oriented as their input surface. WHY ?

I got out that the U- and V-directions of the input surface play a role here, but from a "normal" user -perhaps naive- viewpoint, I was expecting coincident results between Rhino and GH.

Can I expect a modification in the "Evaluate Surface" component or shall I look for another solution?

Attachments:

140206_Panel_Normals_Test.3dm, 383 KB
Face_N_Vec.ghx, 95 KB

Replies to This Discussion

Permalink Reply by Rutger D on February 7, 2014 at 10:01am

Often the surfaces are reparameterized when evaluating them.. not sure if i'm correct but it works in this case.

Permalink Reply by Jaime Sanchez-Alvarez on February 8, 2014 at 11:18am

Rutger, thanks for looking at the problem. I tried reparameterizing the surface at the two components as you showed, but I got the same (wrong) result of mixed normal directions. I even tried reparameterizing at the very beginning at reading the input surfaces, but also got the same result. I am using GH 0.9.0069. How did you get it right?

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