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GeoZarr SWG Monthly Meeting, 6 May 2026 ​

Meeting Purpose ​

Discuss convention governance, resolve open issues, and align on the GeoZarr / CF relationship.

Key Takeaways ​

  • Convention governance. A meeting with the Zarr Steering Council is needed to resolve governance issues (persistence, versioning, registration) before the GeoZarr V1 release.
  • Proj convention. The GeoProj repo will be renamed to Proj, and the convention name will drop the colon (proj: becomes proj) to improve clarity. The namespace prefix (proj:code) remains.
  • Sentinel-1 support. Patrick is developing a "CS convention" to support complex radar data (e.g., Sentinel-1) by implementing OGC's "referencing by coordinates" standard using CF constructs.
  • CF interoperability. A formal CF roadmap is required before the June OGC submission, as a full interoperability solution is not feasible by then.

Topics ​

Convention governance and maintenance ​

  • Problem. Patrick raised concerns about the current convention framework, including:
    • Lack of a clear convention approval process.
    • No guarantee of long-term persistence (10+ years) for convention specs.
    • Ambiguous versioning and change tracking.
    • Flawed registration schema that allows non-machine-readable spec URLs as identifiers.
  • Clarification. The discussion covers two scopes:
    • Zarr Conventions: a cross-discipline framework.
    • GeoZarr Conventions: a specific list of conventions for OGC standardization.
  • Path forward.
    • Zarr Steering Council meeting: Max will schedule a meeting to discuss the framework's future and resolve the attributes vs. top-level conventions key debate.
      • Rationale: The current attributes placement avoids a ZEP (Zarr Enhancement Proposal), which historically stalls.
    • UUID as identifier: The UUID is the required, hosting-agnostic identifier. The schema will be updated to reflect this; the spec/schema URL becomes optional.
    • Maturity and versioning: The group will review existing proposals (PR for maturity levels, Issue #102 for versioning) to define consistent standards for GeoZarr.
    • Hosting and persistence: Issues will be opened proposing Zenodo plus HTTP distribution to guarantee long-term persistence.
    • GeoZarr convention approval: The process will be documented in the GeoZarr spec, using a consensus-driven approach via GitHub issues, with inclusion criteria drafted by Max.

Proj convention (V1 release) ​

  • Repo name. The GeoProj repository will be renamed to Proj to match the convention's name.
  • Convention name. The colon will be dropped from the convention name (proj: becomes proj) to improve clarity. The namespace prefix (proj:code) remains.
  • CRS preference. The group will adopt Manuel's proposal to recommend a preference order (e.g., WKT2) for reading/writing when multiple CRS representations are present.
  • OGC terminology. Patrick will open an issue to align the Proj spec with OGC terminology (e.g., "Projection Authority" is not a standard term).
  • Transform order FAQ. An FAQ entry will be added clarifying that transform order uses matrix algebra (top-left convention).

Spatial convention ​

  • Sentinel-1 support. Konstantin flagged that the current spec cannot describe Sentinel-1 data (axes: zero-Doppler time, slant range).
    • Solution: Patrick is developing a "CS convention" based on OGC's "referencing by coordinates" standard, using CF constructs.
    • Outcome: This convention is expected to enable GeoZarr to read approximately 90% of CF-compatible NetCDF data.
  • 3D language. The group must either remove 3D language or specify its inclusion in the spec.

Multiscales convention ​

  • Layout ordering. The group rejected requiring a "finest to coarsest" layout order.
    • Rationale: Ordering is ambiguous with non-square scales or mixed CRS, and enforcing it creates an unnecessary burden on producers and validators.
  • Composition rules. A revision to the Multiscales composition rules will be proposed.
  • V1 scope. Multiscales for vector data and Tile Matrix Set compatibility are deferred from the V1 release to focus development.

GeoZarr and CF relationship ​

  • Context. Jonathan Gregory (CF Committee) requested a GeoZarr / CF relationship plan by June for Zarr V1 inclusion.
  • Status. A full solution is not feasible by June.
  • Path forward. Max will prepare a formal response and propose a roadmap, seeking buy-in from CF leadership (Governance Panel, CF Committee).

Next Steps / Action Items ​

  • Max
    • Schedule a call with the Zarr Steering Council on convention governance; invite Patrick.
    • Open PRs to rename the GeoProj repo to Proj and update the convention name (proj: becomes proj).
    • Open PRs to update the Zarr Conventions spec:
      • Make UUID the required identifier; spec/schema URL optional.
      • Document the GeoZarr convention approval and inclusion-criteria process; ping Patrick and the GeoZarr group for feedback.
    • Open issues on convention hosting and persistence; propose Zenodo plus HTTP distribution.
    • Schedule a dedicated discussion on registration and transform order.
    • Schedule a call with Patrick on NCI / NCMT.
    • Schedule a call with Manuel on Sentinel-1 EOPF visualization.
    • Draft a formal response and roadmap for the GeoZarr / CF relationship.
    • Send a poll to find a better recurring meeting time.
    • Post these minutes to the Google Group and the OGC / CNG Slack.
  • Patrick
    • Open an issue to align Proj-spec terminology with OGC standards.
    • Share the "CS convention" draft with Konstantin within two weeks; publish and share the link with the group.
  • Konstantin and Patrick
    • Meet to discuss the "CS convention" for Sentinel-1 support.
    • Report findings at the next SWG meeting (June); CS-convention readout is on the agenda.
  • All
    • Review and comment on open issues for the Proj, Spatial, and Multiscales conventions.

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