meta data handling in monai.transforms

[wyli]

initial discussion meeting notes,
the goal was to identify areas of interest (without making design decisions)

• user cases
  • important to be aware of the physical coordinate system in the workflow
  • visualisation
  • lazy resampling (implement stacked spatial transforms as coordinates ops + resampling #112)
  • in annotation tools (e.g. MONAILabel) for exchanging data/annotation
  • real time applications
• design options
  • create python classes to maintain data+metadata via object-oriented methods
  • traceable transforms + metadata dictionaries
  • pytorch named tensor?
  • using an existing toolkit (e.g. ITK) as the backend directly?
• considerations
  • unit of transforms (voxel? physical unit throughout the project?)
  • all transforms should inherit Traceable
  • "raw" header from image files, additional "channel dim" key, "filename/subject id" key

the next meeting is to discuss a "minimal viable product".

CC @rijobro @holgerroth @Nic-Ma