The ChNodeBody constraint implememnts the ChPhysicsItem::GetAssetFrame() method, so that it can be visualized in 3D viewing systems as a box or sphere (or whatever asset that can be added).
Fixed the problem with ChNodeBody.h header being included in two demos (but such header was moved to unit_FEM recently). Btw it was not necessary to include it.
Better interface to B matrix computation for FEM. The member can be called to fill an external B matrix reference, not only for the N copies stored in the element.
Work in progress with FEM visualization... not yet fully functional, though.
Merge branch 'develop' of https://github.com/projectchrono/chrono into develop