Get volume of intersecting Brep

Owkey, this started out as a, for me, simple vb exercise. I have a simple problem.

2 breps intersecting, I want to know the volume of the intersection.

So I opened the RhinoCommon page and started combining things. This is where it went wrong...

So far I got:

Private Sub RunScript(ByVal cone As Brep, ByVal centerpoint As Point3d, ByVal points As Point3d, ByVal boundingbox As Brep, ByRef A As Object)

'move the cone to the point location

cone.Translate(points - centerpoint)

' get the intersection

Dim result As brep() = rhino.Geometry.Brep.CreateBooleanIntersection(cone, boundingbox, 0.001)
'get the volume of the intersection

Dim volume As Double = rhino.geometry.VolumeMassProperties.Compute(result(0))

A = volume

End Sub

Both the intersection as the volumeMass give me errors.

Any suggestions?

Replies to This Discussion

Permalink Reply by David Rutten on July 19, 2011 at 10:29am

Hi Sander,

Brep.CreateBooleanIntersection() operates on collections of Breps, not individual breps. I'm assuming you get the following error:

error: Unable to cast object of type 'Rhino.Geometry.Brep' to type 'System.Collections.Generic.IEnumerable`1[Rhino.Geometry.Brep]'. (line: 86)

This basically translates to: "I wanted a collection of Breps and you've given me a single brep". You'll need to put your cone and boundingbox into a collection. Easiest is to make an inline array:

Dim result As Brep() = Brep.CreateBooleanIntersection( _

New Brep() {cone}, _

New Brep() {boundingbox}, _

0.001)

I concur it should probably work on individual breps as well, I'll add those overloads to RhinoCommon.

-----------------------------

Dim volume As Double = rhino.geometry.VolumeMassProperties.Compute(result(0))

This is wrong. VolumeMassProperties.Compute() does not return a single number. It returns a new instance of the VolumeMassProperties class, which contains the volume, but also the error, the centroids, the moments of inertia and so on and so forth.

Dim vp As VolumeMassProperties = VolumeMassProperties.Compute(result(0))

A = vp.Volume

David Rutten

david@mcneel.com

Poprad, Slovakia

Permalink Reply by Sander Mulders on July 19, 2011 at 12:25pm

Ahh now its finally getting to me. Still trying to figure out how to interpret and apply the Rhino.Common tools. Thanks for the quick response.

Now I only need to figure out a way to do this for 1000+ objects without waiting too long :) Lets see what the rhino.common has to offer.

Permalink Reply by Sander Mulders on July 19, 2011 at 1:51pm

Hmm just when I thought I had it... I lost it again...

Now the issue is with the brep.closestPoint

Dim result As New list (Of Boolean)

Dim check As Boolean = False

For i As Integer = 0 To points.Count() - 1

check = False

For k As Integer = 0 To objs.Count() - 1

Dim closestPt As point3d = Nothing
Dim ci As ComponentIndex = Nothing
Dim s As Double = Nothing
Dim t As Double = Nothing
Dim normal As Vector3d = Nothing

If (objs(k).ClosestPoint(points(i), closestPoint, ci, s, t, maxDistance, normal)) Then

check = True
Exit For
End If

Next

result.Add(check)

Next

A = result