[IGSTK-Users] vtkPolyData transparency trouble

[Romain Carpentier]

Hi everybody,

I'm currently working on an image-guided neurosurgery application based
on IGSTK. In this application, the visualization widget exposes 3
orthogonal views and a 3D view in which we display several vtkPolyData,
each owning its color and opacity (around 0.5).

The problem is that deciding whether one part of a given vtkPolyData is
behind or in front of a part of another vtkPolyData is sometimes
impossible. This trouble genuinely can be annoying.

This problem is due to the way VTK manages transparency along the camera
view vector through entities' polygons.

I solved the problem in another application (that does not use IGSTK)
by :
1-initially using a vtkDecimatePro to cull many "useless" polygons
generated by our tools for the patient's head or brain
2-applying a vtkDepthSortPolyData to the output at each frame : this
uses the camera view vector to sort polygons which are then displayed
without any ambiguity. The first step (decimation) had to be set and
leads us to a trade-off between surfaces' quality and framerate. 

My question is : does IGSTK already offer any solution to this problem?
If not, how could I solve it using IGSTK?

Perhaps, a modification in igstkMeshObjectRepresentation and igstkView
following the solution above could solve it...

Thank you very much for this great toolkit,

Romain Carpentier
Unité/Projet VisAGeS U746
INSERM/INRIA/CNRS/U. de Rennes I
IRISA
Campus de Beaulieu, 35042 Rennes Cedex, France

email: romain.carpentier at irisa.fr
http://www.irisa.fr/visages/