Sort Vertices Clockwise

Replies to This Discussion

Permalink Reply by Devang Chauhan on August 24, 2017 at 2:02am

I am trying to do this using Python, but C# or a pseudo code will work too.

Permalink Reply by Petras Vestartas on August 24, 2017 at 2:12am

Yeah it is pain in the ass to do this, I was trying to find method to unify mesh windings similarly as weaverbird does.https://gamedev.stackexchange.com/questions/30537/how-to-determine-...

No luck.

However if you are limited to 1 polyline only.

For meshes I used this approach

You could do is Mesh.GetNakedEdgePointStatus() to get all the vertices’ (not topology vertices!) naked edge statuses. Then start at one vertex and enumerate all edges that radiate from that vertex. Take the edge that has a naked opposite vertex and keep going from that vertex until you reach the beginning.

The same logic can be applied to breps.

You can apply graph method, but I believe just looping thought edges with its adjacency is a straight forward process.

Permalink Reply by peter fotiadis on August 24, 2017 at 4:06am

Petras,

For polylines check Polyline_measure...

For meshes check the approach used in MakeTrees Method: (MTV.SortEdges(index))

Attachments:

• Mesh_MTV_VS_MV_vertexIndices_V2A.gh, 141 KB
• Polyline_measure_angles_V1.gh, 135 KB

Permalink Reply by Chapulin Colorado on August 24, 2017 at 8:36am

Hey Peter!

nice to see you are back!

Permalink Reply by Anders Holden Deleuran on August 24, 2017 at 2:40am

Here's the method I usually use for this (as you can see, for concave polygons the center point approach is indeed sensitive, so you may need to come up with a heuristic to deal with your specific case):

Edit: This concave hull approach might also fit your needs.
EditII: I think I might have misunderstood the problem, my bad, more coffee :)

Attachments:

• 160825_SortPointsRadially_GHPython.gh, 3 KB

Permalink Reply by Petras Vestartas on August 24, 2017 at 3:00am

Concave hull example is really nice.

Permalink Reply by Devang Chauhan on August 24, 2017 at 3:22am

Thank you, Petras and Anders for prompt responses. I am looking into what you both shared. Will post back where I end up. Appreciate the support.

Permalink Reply by Pieter Segeren on August 24, 2017 at 3:53am

Hi Devang, could a gh definition pass as pseudo code too? In the example I Also cut a hole in the (already trimmed) surface:

If you start writing a script I would duplicate the BrepLoops (not available through vanilla gh), and sort the verts along those: they'll be sorted CCW for the outerloops, and CW for the innerloops (note: reverse of what you asked for). I think that's the 'safest' approach.

Permalink Reply by Devang Chauhan on August 24, 2017 at 4:27am

Hi Pieter,

Although I am trying to do this in Python, your example is a great help. I will try to mimic this logic in Python. Will post how it turns out.

Thanks a lot!

Permalink Reply by Richard Schaffranek on August 24, 2017 at 10:04am

Maybe I am missing a point, but:

1. If you have a surface you can take the naked edges and join them.

2. You can take the first two lines as vector and compute the cross product.

3. Then check if the resulting Vector looks up or down e.g. computing the dot product against Z

4. resort all down or up vectors -> resulting points are all sorted clockwise or counterclockwise...

This works as long as you have a direction Z....

enjoy Richard

Attachments:

• sortingClockwise....gh, 16 KB

Permalink Reply by Iremnur Tokac on July 10, 2018 at 2:25pm

Hi there! 

I encountered the same issue. I am using C# to iterate transformations of an initial Brep (or simply a Brep) by using its vertices' information. But, generated Breps are not following the same index order as the first one. Therefore, the code is not working as I want it to be. 

I wonder how did you solve this issue at the end? Thanks :)