How to transform coordinate between world coordinate system and volume(data) coordinate system

ear VTK,

Could you please share more information about how to transform coordinate between world coordinate system and volume(data) coordinate system?

In my project, a NIFTI volume data is loaded.And I displayed this volume based on “vtkGPUVolumeRayCastMapper”.

In this case, I am not quite clear about the difference between world coordinate and volume coordinate.
When I picked a point based on “vtkPropPicker”, I think this point belongs to world coordinate.
How can I transform it to volume space?

Thank you so much for your help!
Jiangyuan Zhu