[vtkusers] Pick a position on an isosurface based on volume rendering

[LingXiao Zhao]

Dear all:

Is there anyone who can help me with the problem of picking a position
on an isosurface? The visualization is based on the VTK volume
rendering classes:

1) vtkStructuredPoints as the dataset;
2) vtkVolumeRayCastIsosurfaceFunction as the transfer function;
3) vtkVolumeRayCastMapper as the mapper;
4) vtkVolume as the Prop3D objects.

The problem is how to pick a position on such a generated isosurface.
Cause vtkPicker or similar existing functionalities only handle the
polygonal surface mesh. What's the pipeline to do vtkPicker in Volume
Rendering? I am looking forward for your hints.

Thanks a lot!
Lingxiao