A more efficient way to cull points by plane

Hello,

I have a large 3D grid of points an would like to "slice" it with a plane surface that I have drawn in Rhino, i.e. delete all points that are "below" the surface.

I have succeeded using the attached parallel script, but it is still too slow in my case. I need to be able to move the reference surface around in Rhino and get as quick a feedback in GH as possible.

def closestpt(point):
pattern = []

rc, u, v = srf.ClosestPoint(point)
surface_xyz = srf.PointAt(u,v)
dirPos = rs.PointAdd(surface_xyz, surface_normal)
dirNeg = rs.PointSubtract(surface_xyz, surface_normal)
dist = rs.Distance(surface_xyz, point)
if (rs.Distance(point, dirPos) > rs.Distance(point, dirNeg)): bool = False
else: bool = True
pattern.append(bool)

return pattern

surface_normal = rs.SurfaceNormal(srf, (0,0))
pattern = ghpythonlib.parallel.run(closestpt, pts, True)

Any ideas?

Cheers,

Max

Attachments:

srfCP.gh, 8 KB

Replies to This Discussion

Permalink Reply by Daniel González Abalde on November 8, 2016 at 7:06am

If instead of a surface you use a plane, you can use the .ValueAt(pt) method, if it is less than zero then cull the point.

In one line: pattern = Pln.ValueAt(pt) > 0

Permalink Reply by Max Marschall on November 8, 2016 at 7:42am

Much better, thanks!

Permalink Reply by Anders Holden Deleuran on November 8, 2016 at 7:42am

Hi Max, I couldn't get your file to run (missing internalized geo and I think it might be written in Rhino 6 WIP, maybe?). Anywho, a couple of observations:

1) The method itself will likely run faster using some simple vector math and RhinoCommon (basically, to check if a point is above a plane: Calculate the dotproduct between the plane Z-Axis and a vector from the plane origin to the point. If this is negative you're below, else above the plane).

2) The cost of inputting/outputting large lists of objects can be very expensive (see this thread for tips). Best way to get around this is to encapsulate the logic inside your GHPython components as much as needed and not input/output more than you have to. Alternatively you can wrap the data from one component to the next in something which won't expose the data to GH. A third option is to use the PointCloud class or even the Volvox pointcloud. Both should severely speed this up.

3) Of course multithread it once it you find the best solution for you (if it's still too slow ;)

Attached a file exemplifying some of this..

Edit: Didn't see Daniel's answer, using Plane.ValueAt(pt) method will be even faster than calculating it yourself via Python.

Attachments: