API: center of mass calculation of parts in an assembly

Hello,

I have an assembly with N parts, and am trying to output the center of
mass of each part, with respect to the assembly coordinate system to a
file. I have found some examples online, and have begun to craft a
VBA script, which is shown below.

Now, the code below outputs the center of mass of each part, with
respect to that part's coordinate system (each part is a cube of
dimension 4cmx4cmx4cm, so the center of mass is reported as
(0.02,0.02,002)). Here is the output of the code:

%Begin Output
block-4,0.02,0.02,0.02,0.000064
block-3,0.02,0.02,0.02,0.000064
block-2,0.02,0.02,0.02,0.000064
block-1,0.02,0.02,0.02,0.000064
block-5,0.02,0.02,0.02,0.000064
% End Output

Any ideas on how to change the below code so that the output for each
part is the center of mass with respect to the assembly coordinate
system?

Thanks in advance,
Paul Rebillot

% Begin Code
Option Explicit

Sub main()

Dim swApp As SldWorks.SldWorks
Dim swAssy As SldWorks.ModelDoc2
Dim swGroup As Variant
Dim count As Integer
Dim swComp As SldWorks.Component2
Dim swCompModel As SldWorks.ModelDoc2
Dim swCompBody As SldWorks.Body2
Dim vMassProps As Variant
Dim i As Integer
Dim status As Long
Dim tempOutput As String
Dim partName As String

Set swApp = Application.SldWorks
Set swAssy = swApp.ActiveDoc
swGroup = swAssy.GetComponents(0)
count = swAssy.GetComponentCount(0)

Open "C:\test.txt" For Output As #1

For i = 1 To count
Set swComp = swGroup(i - 1)
Set swCompModel = swComp.GetModelDoc

' Get name of component
partName = swComp.Name
' Use this method to get component mass properties
' Currently, this outputs CoM wrt to individual component
coordinate system.
' need to output wrt to assembly coordinate system, or
transform to this system.
vMassProps = swCompModel.Extension.GetMassProperties(2,
status)
' Output to file
tempOutput = partName & "," & vMassProps(0) & "," &
vMassProps(1) & "," & _
vMassProps(2) & "," & vMassProps(3)
Print #1, tempOutput
Next i

Close #1 ' Close file.

End Sub
% End Code

 

You have to take the transformation matrix from each component, and use
matrix algebra to transform the coordinates to the assembly coordinate
system. There is helper classes/methods in the SW api (MathPoint,
MathVector, Matrix etc) to make things easier. If you have no idea what this
means, you should try to learn some basic matrix/vector stuff first; there
are lots of great tutorials in the net (use google and search for eg. 3d
transforms).

Basically the transform matrix of a component contains information about the
position and the orientation of a component, and you can use matrix algebra
to transform coordinates beetween component/assembly levels. Note that the
component may be located in a sub-assembly, so this has to be done step by
step for each assembly level.

Hope this helps!

-h-

 

Thanks for your help. I do know how to do this - just hoping that
there was a way to bypass the coordinate transformations, and have SW
output this for me directly.

Thanks again!
Paul