Triangulate outer points

Hello everyone :)

I am trying to find a solution for the following problem: I have a set of points out of which I want to make a brep/mesh to test if a different point is inside or outside of this brep. After desperately trying everything I know, I am stuck with no more possibilities to try out.

The current approach is to triangulate all outer points, out of which I would then make surfaces and then join them into my wanted brep. The problem is that I cannot find a suitable triangulation for this problem. It should basicaly be like the Delauney triangulation, but all the way through.

Please have a look on the picture to understand my problem better (its not as clear as i though it would be). The Rhino and GH files are attached as well.
I hope someone can help me :(

Attachments:

Replies to This Discussion

Permalink Reply by David Rutten on April 28, 2017 at 4:55am

I think what you are looking for is a 3D Convex Hull. Grasshopper does not have a native component for this, but I'm pretty sure various people have managed this in the past.

Permalink Reply by Azra Gradincic on April 28, 2017 at 5:31am

Thats exactly what I´m looking for and thats basically what I´m trying to recreate somehow :)

Permalink Reply by peter fotiadis on April 28, 2017 at 5:00am

Delauney works on "flattish" collections. Although your sample pic has few points ... in general you'll need some Ball Pivot triangulation. If the points are a lot (for instance LIDAR stuff) you'll need a quite good, fast and hopefully bug free BP.

If memory serves well there's some GH add-on that attempts BP triangulation (but I can't recall details nor the name: but I do remember that I've tested it - some years ago - and it works [in most of cases]).

Permalink Reply by Azra Gradincic on April 28, 2017 at 5:37am

In general, there shouldnt be too many points per knot, but there will be many knots to calculate :) If you remember what add-on it was, I would be very thankful for any hint as I am a novice in GH and don´t think I will figure it out on my own.
I´ll search for the ball pivot for now, maybe I come across sth that might help :)

Permalink Reply by peter fotiadis on April 28, 2017 at 5:46am

Indeed you can't do that without a certain experience in coding. But I'm sure that someone else who may read this could provide the name/link.

Unfortunately I can't provide my BP since they are all strictly internal (only for use inside the practice)

Permalink Reply by peter fotiadis on April 28, 2017 at 7:44am

WAIT A MINUTE:

This doesn't require BP stuff. I've used a "similar" thingy (made for totally different purposes) and it works OK (required Sandbox).

I could easily modify the code in order to work far more effectively (Notably: never accept a triad that contains the "center" point etc etc).

So ... post the sum of all connections of yours in order to test the thing against the real McCoy

Attachments:

Graphs_FindTriads_V1B_DEMO-PUBLIC.gh, 134 KB

Permalink Reply by Azra Gradincic on May 2, 2017 at 10:47am

Wow, thank you so much for your effort!
I´ve managed to find a Ball Pivot function in Milkbox and it works quite fine for now. I dont know how it will do once I draw a bigger modell, so I might come back to you if necesarry :)
Thanks a lot!

Permalink Reply by peter fotiadis on May 2, 2017 at 10:50am

If you have a kind of graph and you want to do that for each vertex (meaning few - more or less - edges but many vertices) then BP is an overkill ... but if it works why bother?

Permalink Reply by David Stasiuk on May 2, 2017 at 1:46pm

The plug-in Starling has a solid component for making convex hulls.

Permalink Reply by Michael Pryor on May 3, 2017 at 8:19am

As Stasiuk mentioned, starling has a nice 3d Convex hull component. Additionally, here is a quick hacky way I use sometimes just to imagine the point cloud volume.

Attachments:

MeshPoints.gh, 9 KB

Permalink Reply by peter fotiadis on April 28, 2017 at 8:29am

BTW: If by accident we are talking about a 3d graph (meaning that you have it already on hand) this is also easy:

See this "similar" (kinda) case: a demo mini graph (resembling some random demo truss) where the axis to axis angles that are less that the current node angle (between the axis of the "solid" tubes) are marked red (they are tri meshes for speed). This works using connectivity data trees (in the public version Sandbox is also required) and it could be very easily modified to do what do you want skipping the angle calculation/checks etc (meaning no proximity required etc etc). Since all the work is done by "comparing" integers (indexes) this is real-time fast no matter the amount of nodes in the graph.

The bad news are the obvious: code only I'm afraid (not ideal at all for a novice).