intersection of three spheres (get a solid3d)

[Anonymous]

The  first and second figure shows three spheres. What I wanted to customize is to get the common intersection region among the three spheres(seen in third figure). Below is my code.

Imports System
Imports System.Runtime.InteropServices
Imports System.Drawing
Imports Autodesk.AutoCAD.Runtime
Imports Autodesk.AutoCAD.DatabaseServices
Imports Autodesk.AutoCAD.Geometry
Imports Autodesk.AutoCAD.ApplicationServices
Imports Autodesk.AutoCAD.EditorInput
Imports Autodesk.AutoCAD.ApplicationServices.DocumentExtension

{code here}

Dim bt As BlockTable = tr.GetObject(db.BlockTableId, OpenMode.ForRead)
Dim btr As BlockTableRecord = tr.GetObject(bt(BlockTableRecord.ModelSpace), OpenMode.ForWrite)

Dim its_points As Point3dCollection = New Point3dCollection()
its_points = Getcriticalpoints(pt1, pd11, pd12, pt2, pd21, pd22, pt3, pd31, pd32)
Dim n_of_itspts As Integer = its_points.Count
Dim i As Integer = 0



For Each pt3d As Point3d In its_points
Dim ptt As Point3d = pt3d
Dim sph As Solid3d = New Solid3d()
sph.CreateSphere(rad)
sph.TransformBy(Matrix3d.Displacement(ptt - Point3d.Origin))
btr.AppendEntity(sph)
tr.AddNewlyCreatedDBObject(sph, True)
sphere_ID(i) = sph.ObjectId
i = i + 1
Next

Dim intersection_points1 As Point3dCollection = New Point3dCollection()
Dim intersection_points2 As Point3dCollection = New Point3dCollection()

Dim sph1 As Solid3d = tr.GetObject(sphere_ID(0), OpenMode.ForRead)
Dim sph2 As Solid3d = tr.GetObject(sphere_ID(1), OpenMode.ForRead)
Dim sph3 As Solid3d = tr.GetObject(sphere_ID(2), OpenMode.ForRead)

sph1.IntersectWith(sph2, Intersect.OnBothOperands, intersection_points1, IntPtr.Zero, IntPtr.Zero)
sph1.IntersectWith(sph3, Intersect.OnBothOperands, intersection_points2, IntPtr.Zero, IntPtr.Zero)

btr.AppendEntity(sph1)
tr.AddNewlyCreatedDBObject(sph1, True)
tr.Commit()

end using
end sub

Private Shared Function Getcriticalpoints(ByVal center1 As Point3d, ByVal rad1 As Double, ByVal height1 As Double, ByVal center2 As Point3d, ByVal rad2 As Double, ByVal height2 As Double, ByVal center3 As Point3d, ByVal rad3 As Double, ByVal height3 As Double) As Point3dCollection

    Dim result As Point3dCollection = New Point3dCollection

    Dim line12 As LineSegment3d = New LineSegment3d(center1, center2)
    Dim line13 As LineSegment3d = New LineSegment3d(center1, center3)

    Dim line12_dis As Double = line12.Length : Dim line13_dis As Double = line13.Length

    Dim circ1 As CircularArc3d = New CircularArc3d(center1, Vector3d.ZAxis, rad1)
    Dim circ2 As CircularArc3d = New CircularArc3d(center2, Vector3d.ZAxis, rad2)
    Dim circ3 As CircularArc3d = New CircularArc3d(center3, Vector3d.ZAxis, rad3)

    Dim its212() As Point3d = circ2.IntersectWith(line12)
    If (Not (its212) Is Nothing) Then
        Dim point1 As Point3d = New Point3d(its212(0).X, its212(0).Y, its212(0).Z + height2)
        result.Add(point1)
    End If

    Dim its313() As Point3d = circ3.IntersectWith(line13)
    If (Not (its313) Is Nothing) Then
        Dim point2 As Point3d = New Point3d(its313(0).X, its313(0).Y, its313(0).Z + height3)
        result.Add(point2)
    End If

    If line12_dis >= line13_dis Then

        Dim its112() As Point3d = circ1.IntersectWith(line12)
        If (Not (its112) Is Nothing) Then
            Dim point3 As Point3d = New Point3d(its112(0).X, its112(0).Y, its112(0).Z + height1)
            result.Add(point3)
        End If

    Else

        Dim its113() As Point3d = circ1.IntersectWith(line13)
        If (Not (its113) Is Nothing) Then
            Dim point4 As Point3d = New Point3d(its113(0).X, its113(0).Y, its113(0).Z + height1)
            result.Add(point4)
        End If

    End If

    Return result

End Function

end class
end namespace

the debug process will be broken at 

ph1.IntersectWith(sph2, Intersect.OnBothOperands, intersection_points1, IntPtr.Zero, IntPtr.Zero)

with the message

An exception of type 'Autodesk.AutoCAD.Runtime.Exception' occurred in AcdbMgd.dll but was not handled in user code

Additional information: eNotImplementedYet

If there is a handler for this exception, the program may be safely continued.

Can some autocad customization experts help me with this?

[Anonymous]

Solved.