AutoCAD VBA: Selecting objects - vba

Question

I have a 3D model of an intricate chimney which is essentially a cylindrical tube with decorative features. I'd like to write a VBA script which find the section properties at several points along its length but I'm not really sure how to do it.
From online searches, I've managed to write a code which puts in a section at a point which I can then run MASSPROP on but I'm not quite sure how to finish it off... I think I'm only one line of code away. I just need to select the section that I've just created.
My almost complete code is below with a comment on the line that I need help with.
Public Sub Section()
Dim SolidObject As Acad3DSolid
Dim NewRegionObject As AcadRegion
Dim PlaneOrigin As Variant
Dim PlaneXaxisPoint As Variant
Dim PlaneYaxisPoint As Variant
Dim PickedPoint As Variant
On Error Resume Next
With ThisDrawing.Utility
.GetEntity SolidObject, PickedPoint, vbCr & "Select solid to cut."
If Err Then
MsgBox "Selected solid must be a 3DSolid"
Exit Sub
End If
PlaneOrigin = .GetPoint(PickedPoint, vbCr & "Select point to define origin.")
PlaneXaxisPoint = .GetPoint(PickedPoint, vbCr & "Select point to define x-axis.")
PlaneYaxisPoint = .GetPoint(PickedPoint, vbCr & "Select point to define y-axis.")
Set NewRegionObject = SolidObject.SectionSolid(PlaneOrigin, PlaneXaxisPoint, PlaneYaxisPoint)
End With
ThisDrawing.SendCommand ("qaflags" & vbCr & "2" & vbCr) 'This is needed for the operation
ThisDrawing.SendCommand ("massprop" & vbCr)
'How do I select my NewRegionObject???
ThisDrawing.SendCommand (vbCr & vbCr & "y" & vbCr & vbCr & "y" & vbCr)
End Sub
If I can get this code to run MASSPROP with my newly created section fine I should be able to adapt it to do the process automatically at several points along the chimney so I think I'm only one line of code off.
Thanks for your help,
Tom

Answer 1

you'd better exploit Autocad Object Model:
Dim minPoint As Variant, maxPoint As Variant
Set NewRegionObject = SolidObject.SectionSolid(PlaneOrigin, PlaneXaxisPoint, PlaneYaxisPoint)
With NewRegionObject
MsgBox "Area: " & .Area
MsgBox "Perimeter: " & .Perimeter
.GetBoundingBox minPoint, maxPoint
MsgBox "Min Point coordinates: (" & minPoint(0) & "," & minPoint(1) & "," & minPoint(2) & ")"
MsgBox "Max Point coordinates: (" & maxPoint(0) & "," & maxPoint(1) & "," & maxPoint(2) & ")"
MsgBox "Centroid coordinates: (" & .Centroid(0) & "," & .Centroid(1) & ")"
MsgBox "Moments of Inertia: (" & .MomentOfInertia(0) & "," & .MomentOfInertia(1) & "," & .MomentOfInertia(2) & ")"
'.. and so on
End With