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JSON based scene file format

Key Investigators

• Davide Punzo (freelancer, DNA-HIVE, France)
• Andras Lasso (Queens University, Canada)

Project Description

Overview

The primary objective of this feature is to introduce support for JSON format to enable writing and reading the full MRML scene file and its nodes. This serves as preparatory work for:

1. Supporting a more structured format for the MRML file with explicit datatypes.
2. Providing APIs in Slicer to facilitate collaborative features, such as retrieving and updating the status of individual nodes.

With this setup, we would start a first step for future adoption and compatibility with standards like OpenUSD and real-time collaborative toolkits (e.g. Omniverse). For example, having MRML structured in JSON will make it much easier to convert nodes to OpenUSD.

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Implemented Features

• Node Status Printing: Nodes can now output their state in JSON format using the WriteJSONToString method. For example, in the Python console:

  crosshairNode.WriteJSONToString()
  

  Output:

  {
    "Crosshair": {
      "id": "vtkMRMLCrosshairNodedefault",
      "name": "Crosshair",
      "hideFromEditors": true,
      "selectable": true,
      "selected": false,
      "singletonTag": "default",
      "crosshairMode": "NoCrosshair",
      "crosshairBehavior": "OffsetJumpSlice",
      "crosshairThickness": "Fine",
      "crosshairRAS": [0.0, 0.0, 0.0]
    }
  }
  

• Node State Reading/Updating: Nodes can now read or update their state (either fully or partially) from a JSON string. For example:

  a.ReadJSONFromString('{"Crosshair":{"crosshairRAS":[100.0,100.0,100.0]}}')
  

• Scene-Level JSON Format Support: The format for the entire MRML scene is controlled by a macro:

  vtkMRMLScene::SetUseJSONFormat(true);
  

  When enabled, the scene file will be output in JSON format. For example, the attached sample file demonstrates the current output structure.

Objective

1. Get feedback on the current preliminary implementation PR and work a final design for the JSON based node status/scene file format.

Approach and Plan

1. Have a meeting/demo with people interested for colletting feedback.
2. Work on the final design of the JSON based node status/scene file format.

Progress and Next Steps

Illustrations

No response

Background and References

PR