I want to position a plane in an 3D picture (Skull). How I navigate in a 3D perspective? The mouse has 2D coordinates. If I use pickpoint I will be limited to the bone (skull) points to position the plane.
It is not entirely clear what you are trying to achieve, but it seems to be an application-level feature, which you can copy from open-source VTK-based applications, such as ParaView or Slicer. As always, I recommend to build on existing open-source application platforms instead of redeveloping all basic features from scratch.