Strange Normals for Surface

Grasshopper
1

Please see attached 3dm and grasshopper file.

The 3dm file contains a surface which represents the bottom of a boat hull. In grasshopper, I have created a rectangle in the XY plane. I then projected the 4 corners of the rectangle upwards in the z-direction and found the projection of those 4 corners on the bottom of the hull surface. I next wanted to find the normal vectors to the surface at each one of those points. I used Evaluate Surface to do this. However, the vectors returned are clearly not normal to the surface. This is not just a matter of the normals being flipped. The normals are pointing in what are clearly the wrong directions. I am wondering if the issues is in the surface itself, but I cannot figure out the issue. See attached screenshot.

Thanks in advance for any help!

2020-12-15_15-42-44
2020-12-15_15-42-441143×547 57.4 KB

Hull_Shape.3dm (156.2 KB)

Position Keel Cooler Project.gh (12.6 KB)

2

missing

You skipped Srf CP (Surface Closest Point) before Evaluate Surface.

Keel _2020Dec16aa
Keel _2020Dec16aa1382×321 74.1 KB

Keel _2020Dec16a.gh (16.8 KB)

Keel _2020Dec16a2
Keel _2020Dec16a21158×566 112 KB

3

Thanks ! I had tried to use Surface Closet Point already without success. But after studying your example, I see that my error was that I had connected the “Point” output from Surface Closest Point to the “Point” input on Evaluate Surface. What I need to do was connect the “UV Point” output from Surface Closest Point to the “Point” input on Evaluate Surface.

Thanks!

Will