Recommended representation of multi-level grid STAC Items/Assets

[fmigneault]

Description

Given a set of grid data with multiple zoom levels, where the tiling is not necessarily square and respects a certain DGGS (Discrete Global Grid System), there does not seem to be an obvious or immediate strategy to represent them.

Are there any known alternatives to below considerations? What would be the recommended strategies?

Considered extensions / STAC spec properties

• https://github.com/stac-extensions/tiled-assets
  • makes sense regarding the tiling and the tiling set could be used for cross-referencing relevant zoom items
  • however, row/col structure typical of square grids that does not make it adequate for other shapes
• https://github.com/stac-extensions/grid
  • allows custom grid:code
  • lacks details about the nesting (how to reference child or parent zoom/level items related to a current item)
  • lacks explicit way to resolve relevant properties zoom/level that describes the specific grid/format
  • see Provide more grid fields stac-extensions/grid#12
• https://github.com/stac-extensions/virtual-assets
  • could be used with vrt:hrefs to list child items that compose a finer level grid
  • not much equivalent definition for parent and neighbor items, and it might be abusing the definition of vrt:hrefs
• https://github.com/stac-extensions/link-templates
  • provided a certain DGGS code, zone IDs can be known in advance and used directly to access a certain position and resolution level, allowing use of preformed URI
  • other templating parameters (eg: for temporal aspects) are less easily predetermined than zone IDs
• STAC Core Spec
  • Items using rel: child (for finer levels) and rel: up (for coarser levels).
    Important to avoid rel: parent reserved for the STAC collection reference.
    Could use rel: down or other instead of rel: child.
  • Might cause too much confusion with the usual cataloguing references, and is not very obvious that it implies a grid
  • Using generic properties for other grid aspects would limit reusability and replicability

Best Practices

Whichever combination / solution that is elaborated should be documented in https://github.com/radiantearth/stac-best-practices

[fmigneault]

@matthewhanson @jbants
Did you get the chance to review this and stac-extensions/grid#12?
I would like to start drafting something in grid extension, but still waiting on your feedback in case anything else should be considered.