I am adding a coordinate system (own class, derived from GroupModel3D) to my scene, and setting its Transform to the transform of the current selected object.
Everything is working fine, except when the object is to big, the coordinate system is inside and because of this not visible. So I like to make the coordinate system topMost, like it is in most CAD-systems.
I searched the internet and I found that simple clearing the z-/depth- buffer would do it (http://www.gamedev.net/topic/297605-how-to-keep-an-object-always-visiblein-front-of-others/) but i don't know how to do this inside HelixToolkit.
Found the Solution in the issues section of helixtoolkit: https://github.com/helix-toolkit/helix-toolkit/issues/226