Finding normal vectors on precise points of a mesh

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Permalink Reply by Claudia on September 18, 2014 at 5:42am

Ok, I've just used this script from David Rutten:

http://www.grasshopper3d.com/forum/topics/line-line-intersestion-pr...

It works, but seems that some curves doesnìt intersect, even if they are part of the same mesh..what can I do?

Permalink Reply by nikos tzar on September 18, 2014 at 7:06am

Hi Claudia,

The curves are actually polylines because they are the intersections between the planes and the mesh faces (press Ctrl+M in grasshopper to see the mesh edges).

Your mesh has quad faces (4 points) and they are not planar so if 2 polylines cross a face from opposite edges then they actually do not intersect. One way to get around this is to triangulate all mesh faces ([Mesh Triangulate] component under Mesh/Analysis Tab). This way all faces will be planar and you will get all the intersection points.

Permalink Reply by nikos tzar on September 18, 2014 at 7:28am

I also noticed that this solution (triangulate mesh faces) actually sorts out your second issue as well (though I can't understand why...).

I would just suggest adding a [cull duplicate points] component because some intersections provide 2 points:

Permalink Reply by Claudia on September 18, 2014 at 9:42am

I was convinced that the quadrangular face were planar, so it didn't make sense to me.

Now it works fine, thank you.

I have only another doubts: how can I exclude the base points from the list of the intersection point? I don't need the cilinders at the base angles.

Permalink Reply by nikos tzar on September 18, 2014 at 9:56am

You could cull the points with Z coordinate close to 0:

Attachments:

• 03_catenary_MOD_11.gh, 29 KB

Permalink Reply by Claudia on September 18, 2014 at 10:00am

Great, you gave a precious help :)