Perimeter points of a topo

im trying to get the perimeter vertices from a topography, is this possible?

The methods i have tried so far pick up all the vertices.


Please show your work, post images or sample files.

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Actually, you don’t have to bother with that, because I am pretty sure that Dynamo doesn’t have any decent Mesh tools that would handle this issue. I checked in the Mesh Toolkit and none of the Mesh topology tools that are there will do the job.

You need to extract mesh naked edges and then just pull points from them. That’s pretty easy to do with something like Grasshopper. You could use Mantis Shrimp and send that Mesh to Grasshopper, do the point extraction there and then send the results back. It’s relatively easy, although unnecessarily convoluted. Dynamo should have a better Mesh library. Period.

Ps. This is an amendment to my statement. It looks like @Andrew_Hannell pointed us all to “IsBoundaryPoint” method that would solve the issue here. Well Done!

You can get a 2d representation of the perimeter fairly easily with a few nodes from Clockwork. For a 3d boundary, I’d have to go with Konrad’s suggestion and go with Grasshopper.

As a free alternative to Gh/Rhino, you could try Blender. You’ll have to extract the topo’s mesh and then export the file as an *.stl (make sure that only the topo mesh is visible in the background preview)

You can then import the STL(you might need to change the units in blender prior to importing), go into edit mode and select all non-manifold geometry:

Getting the data out of blender might be trickier tho…It has a ton of export plugins available and you’ll have to figure out what best works for you…

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You could convert topo mesh to a polysurface and extract perimeter curves


Does this help:


Vikram, This one is perfect thank you!

Nice link. Didn’t know about the “IsBoundaryPoint” method.

Where can I get the two functions which performs “a 2d conv.hull”
I just wanted the 2d projection boundary (not the 3D one) of the subregions I have on my topography, which I think your way could be perfect.

The two nodes are found in the Clockwork package. Springs has a similar method that works directly with points and a specified elevation: Points.ConvexHull2D

I know this was from two years ago, but I am curious as to what UV.ByXY and UV.ConvexHull2D are actually doing.