How to make a random points on a surface?

Replies to This Discussion

Permalink Reply by David Rutten on September 29, 2009 at 11:05am

Why don't you just generate two streams of random numbers (use two similar Random components but with a different seed value), convert those numbers into points using PointXYZ and then feed those points into the SurfaceEvaluate component? If you make sure that the Random domain is the same as the surface domain, you should get random points on the surface.

The density of random points will be affected by the density of the surface isocurves. Placing random points without using UV space requires a different algorithm. Not that much harder to make, but a lot slower to run.

--
David Rutten
david@mcneel.com
Seattle, WA

Permalink Reply by Kyle Blackwell on January 30, 2011 at 12:25pm

Is there a simple way to essentially perform that same thing but within the confines of a 3d volume? basically trying to great a number of random points within a box or volume rather than on a surface.

Permalink Reply by h on January 12, 2014 at 12:29am

I've just tried this. Occasionally, points end up outside the surface - could this have something to do with trimming? Is there a workaround? I cannot figure out how to test if the point is contained within the surface using python.

Thanks

Permalink Reply by David Rutten on January 12, 2014 at 2:06am

For BrepFaces you can test whether a UV point is on or off the trim domain. However when you convert a BrepFace to a Surface you lose the trimming information, so it's important to maintain the original BrepFace.

--

David Rutten

david@mcneel.com

Permalink Reply by h on January 12, 2014 at 9:46am

EDIT: Got it working now, Thanks.

For anyone else reading this, I used rhinoscriptsyntax.IsPointOnSurface

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Whoa. I didn't even know there was a separate type called Brepface. How might I perform that test?

I'm trying to place a point on a surface that is beyond some distance from two other sets of points on the surface.

Here's what I'm working with so far:

def ThrowDart(ListA, DistA, ListB, DistB, Surf_id):
     Done = False
     Uspan = rs.SurfaceDomain(Surf_id,0)
     Vspan = rs.SurfaceDomain(Surf_id,1)
     while not Done:
          UVCoords = [random.uniform(Uspan[0],Uspan[1]),random.uniform(Vspan[0],Vspan[1])]
          Eval = rs.EvaluateSurface(Surf_id,UVCoords[0],UVCoords[1])
          NewPt = Rhino.Geometry.Point3d(Eval)
          # Some kind of surface-region containment test here?

          # test for Distance from ListA and ListB points here

Thanks again for your help. It's been a few months since I've looked at any of this stuff, unfortunately, so I'm out of practice. My eventual goal is to make a GH component that will perform leaf veination type stuff.

Permalink Reply by David Rutten on January 12, 2014 at 10:09am

Ok, python isn't my strong suit, but it looks like you're trying to use RhinoScript like methods in python. There may be a method for testing whether a UV point is on a brepface, I do not know what it is called if it exists.

I can show you how to do this in C# (see attached).

--

David Rutten

david@mcneel.com

Attachments:

• PointOnSurface.gh, 7 KB

Permalink Reply by h on January 12, 2014 at 11:56am

Thank you!