Recap of your meeting with Radiant Earth Foundation

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Nov 3, 2025, 12:03:07 PM (9 days ago) Nov 3

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Meeting Purpose Discuss STAC extensions for multidimensional data and CF conventions. Key Takeaways - DataCube Extension: The proposal to replace variables with bands is paused due to strong community opposition. The current variables structure will be used for now, deferring the larger bands vs. variables discussion to STAC 2.0. - CF Extension: The CF extension will integrate directly into the DataCube extension schema. This requires making description and unit fields mandatory for CF variables to ensure complete metadata. - CF Search Challenge: The DataCube structure makes efficient searching for specific CF variables (e.g., "max wind speed at 10m") difficult, as variable keys are arbitrary. An internal "search acceleration spec" is being considered as a workaround. - Zarr Best Practices: The Zarr Best Practices PR is now open for a one-month community review. It will be updated with concrete examples for key use cases (e.g., single Zarr, CF-Zarr, scene-based EOPF-Zarr). Topics DataCube Extension: variables vs. bands - Proposal: Replace the variables property with bands in the DataCube extension. - Rationale: Unify data channel descriptions under the core bands concept, avoiding duplicate functionality and simplifying data discovery. - Objection: bands is too specific to electro-optical data and doesn't fit generic multidimensional arrays (e.g., NetCDF climate variables). - Decision: Pause the proposal. Continue using the current variables structure. Defer the broader bands vs. variables discussion to STAC 2.0. DataCube Extension: Projection Duplication - Issue: The DataCube extension has a projection field, duplicating functionality from the core Projection extension. - Clarification: The DataCube's projection field is for rare cases where a dimension has a different projection than the asset (e.g., an auxiliary grid variable in a different projection). - Best Practice: Use the core Projection extension by default. Use the DataCube's projection field only when necessary to override the asset-level projection for a specific dimension. CF Convention Extension - Integration: The CF extension will be integrated directly into the DataCube extension schema, not as a separate object. - Mandatory Fields: The description and unit fields will be made mandatory for CF variables. - Rationale: Ensures complete metadata, as not all variables have a standard_name. - Mechanism: The CF extension schema will override the DataCube schema to enforce this requirement. - Cell Methods: The cell_methods property will be an array, with each entry corresponding to a dimension in the DataCube's dimensions array. - Rationale: This structure is simple and maintains the correct order. - Limitation: May not support complex, multi-stage methods (e.g., "average of 5-day daily maximums"). CF Search Challenge - Problem: The DataCube structure makes efficient searching for specific CF variables difficult. - Cause: Variable keys (e.g., wind_speed_at_10_meters) are arbitrary and inconsistent across catalogs. - Impact: Prevents simple CQL queries for common criteria (e.g., "max wind speed at 10m"). - Proposed Workaround: An internal "search acceleration spec" that creates a searchable string from key properties (e.g., air_temperature_2m_instantaneous). - Alternative: A custom STAC API queryable for DataCube properties, which would require significant development. Zarr Best Practices - Status: The Zarr Best Practices PR is now open for community review until the end of November. - Updates: The PR will be updated with concrete examples for three key use cases: - A single large Zarr array - A CF-compliant Zarr array - A scene-based EOPF-Zarr array - Note: The store_link concept will likely be moved from the best practices document to the Zarr extension itself. Next Steps - Emmanuel: Present STACsR sprint results to the EOEPCA Consortium. - Emmanuel: Announce the Zarr Best Practices PR on Slack for community review (due end of Nov). - Emmanuel: Update the Zarr Best Practices PR with concrete examples. - Andy & Emmanuel: Refine the CF extension proposal in the relevant GitHub issue, focusing on the DataCube integration and mandatory fields. - Andy & Francis: Continue discussion on the CF search challenge and potential solutions in the relevant GitHub issue. - Francis: Add comments to the GitHub issues on auxiliary variables and short names.