How to extract a boundary edge from a 3d point cloud

I have produced this point cloud from a shoe sole. I would like to know how to extract the top edge (the top boundary as shown in the second photo) of the point cloud and create a curve out of it using grasshopper.

PointCloud Top Line.3dm (59.8 KB)

Can anybody help me with this?

Thank you.

Unable to open R7 Rhino file in R6 but this might be helpful?

There is a boundary line in the purple group.

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Here the internalized pts: (7.3 KB)

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Ah, thanks. 3D points that make a very poor Delaunay mesh in this case, whereas the points in the other thread were all in the same plane, so no help. Not sure how to solve this one?

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Thank you for the help! Yes the 3D points do not give a good Delaunay mesh. I input the grasshopper definition that you suggested and this was the best result that I got.

Attaching the grasshopper definition in case anybody can take a look at it and advice how to correct it.
Thank you very much :slight_smile: (18.9 KB)

You will need some ball pivoting algorithm.
Maybe with some plugin like cockroach?

By projecting the point cloud to ‘World XY’, I adapted the code to narrow down the points to consider, but need a break so will leave it at this for now. (21.8 KB)

Thank you, Joseph. I took a look at your definition but it seems like you uploaded a different file? :slight_smile:

Looking forward to seeing your solution!

DOH! Fixed in previous post.

P.S. Here’s a thought… :thinking:

Here is something that’s reasonably close and rather “simple”. (32.7 KB)

P.S. Using the cyan curve as an attractor, a few straggler points can be added (yellow). (37.7 KB)

Later… It’s remarkable what Patch can do with this point cloud and the edge curve: (33.7 KB)

Hi Joseph! Thank you for this, it works very well for this case. Now I am trying to apply it to other cases (and understanding your definition while I am at it because I am quite new with grasshopper). I will update you shortly!

I don’t remember all the details myself but the fact that there are four sliders in the GH model indicates that “tuning” is required to make it work. Especially if the overall dimensions are at a different scale.