mesh.IsPointInside always false ?

Replies to This Discussion

Permalink Reply by Danny Boyes on March 26, 2012 at 1:10pm

is it similar to this?

Permalink Reply by Daniel Piker on March 26, 2012 at 3:02pm

This has been broken for a while now. I worked around it by using mesh.ClosestPoint and checking whether the dot product of the normal at that point and the vector from the point to the closest point is positive. It's not ideal though, and a working IsPointInside would be much better.

Permalink Reply by Steve Baer on March 27, 2012 at 11:58am

I see what's going on.  The low level implementation for this function was never completed and just returns false.  I added an item to our internal bug tracker to have the developer who works on this complete the function.

In the meantime, I rewrote the IsPointInside function to get the right answer "most" of the time by

1. Making sure the mesh is solid
2. Using a line-mesh intersector and counting the number of crossings. The the start of the line is the point to test and the endpoint of the line is out beyond the bounding box of the mesh.  An odd number of crossings means the point is inside. This is how the function will work in the next v5 beta (or next grasshopper release for people using V4).

Thanks,

-Steve

Permalink Reply by Mateusz Zwierzycki on April 4, 2012 at 6:35pm

How should I do this intersection ? 

 

Function isPtInside(pt As point3d, msh As mesh) As Boolean
Dim fIdx As int32() = New Int32() {0,0}
Dim isIn As Boolean = False
Dim bbox As New rhino.Geometry.BoundingBox
bbox = msh.GetBoundingBox(True)
Dim fp As New point3d
fp = bbox.FurthestPoint(pt)
Dim vec As New vector3d(fp.X - pt.X, fp.Y - pt.Y, fp.Z - pt.Z)
Dim dist As Double = fp.DistanceTo(pt)
Dim xLine As New Line(pt, vec, dist * 10)
Dim xCrv As New rhino.Geometry.PolylineCurve
xCrv.SetStartPoint(xLine.From)
xCrv.SetEndPoint(xLine.To)

Dim interPt() As point3d = rhino.Geometry.Intersect.Intersection.MeshPolyline(msh, xCrv, fIdx)

If interPt.length mod 2 = 0 then 

isIn = false

else

isIn = true

end if

Return isIn

End Function

This returns an error "Object reference not set to an instance of an object" (I guess that its related to interPt array)

I have to add 2 values (0,0) to fIdx array, otherwise I get a warning that it has no values and it may return a null.

+ you said "Using a line-mesh intersector" ... I cant find it (rhino 4), so I create a polylineCurve to use polyline-mesh intersector. (cant cast line to polyline).. is that how you do it ?

Permalink Reply by David Rutten on April 5, 2012 at 1:12am

Not really sure where your error is, but this is how I'd write it:

Function IsPointInMesh(ByVal point As Point3d, ByVal mesh As Mesh) As Boolean
  Dim box As BoundingBox = mesh.GetBoundingBox(True)
  If (Not box.Contains(point)) Then Return False

  Dim polyline As New Polyline()
  polyline.Add(point)
  polyline.Add(box.Max + New Vector3d(100, 100, 100))

  Dim x As Point3d() = Intersect.Intersection.MeshPolyline(mesh, _

                                 New PolylineCurve(polyline), Nothing)
  If (x Is Nothing) Then Return False
  Return (x.Length Mod 2) = 1

End Function

--

David Rutten

david@mcneel.com

Poprad, Slovakia

Permalink Reply by Steve Baer on April 5, 2012 at 9:08am

The IsPointInside function should now work if you get the latest V5 beta, since it contains the rewrite I mentioned above.

-Steve

Permalink Reply by Daniel Piker on April 5, 2012 at 10:04am

Yes - mesh IsPointInside is working nicely now, as are mesh edge splitting and collapse. Thanks Steve!

Permalink Reply by Matt Gaydon on May 18, 2012 at 8:10am

Hi Guys,

Any chance of seeing mesh.InPointInside command in a script please as having trouble writing the code

Would be great if we can have it as a component.

Thanks

Matt