Do SoViewingMatrixElement and SoViewVolumeElement break bounding box cache?

[Chester Liu <cht@xxxxxxxxxxx>]

Hello,  This has got to be one of those Inventor oddities.
Or maybe I just don't understand what's going on...

The problem:
I have a separator whose render culling field is turned on.

The separator has one child -- a customized transform
node, with the following lines of code in the doAction() method:

     const SbViewVolume & viewVol = 
             SoViewVolumeElement::get(action->getState());

     const SbMatrix & viewMat =
SoViewingMatrixElement::get(action->getState());


The separator reports that the bounding box cache (used for
render culling) is being invalidated.  If I comment out these
lines of code, it's fine.

Why?

This is like the Heisenberg uncertainty principle, where the
act of making an observation changes the thing being observed.

 :)


thanks for any enlightenment!
Chester Liu