Specification should support arbitrary coordinate systems for multiscale data

[emmanuelmathot]

Summary

The current GeoZarr specification has an implicit bias toward web mapping tile schemes and more specifically OGC TMS, which may discourage scientific applications that work with native coordinate reference systems. The specification should explicitly support and encourage the use of arbitrary regular grids for multiscale pyramids.

Current Problem

• Examples in the specification primarily use WebMercatorQuad
• Limited guidance for creating tile matrix sets in scientific projections (UTM, polar stereographic, etc.)
• May inadvertently discourage preservation of native CRS in Earth observation data
• Section 9.7.3 focuses on well-known identifiers rather than custom tile matrix sets

Proposed Solution

1. Add explicit language stating that ANY regular grid system can be used for multiscale pyramids
2. Include diverse CRS examples beyond web mercator (UTM zones, polar stereographic, sinusoidal, etc.)
3. Provide guidance for creating custom tile matrix sets for arbitrary CRS
4. Emphasize scientific accuracy benefits of preserving native CRS

Implementation Evidence

The EOPF GeoZarr implementation successfully demonstrates:

• Creation of "Native CRS Tile Matrix Sets" for arbitrary projections
• Multiscale pyramids working with UTM and other scientific projections
• Proper scale denominator calculations for non-web CRS
• Chunking strategies optimized for native coordinate systems

Specification Sections to Update

• Section 9.7.3 (Tile Matrix Set Representation)
• Section 7.6.1 (Format Mapping and Alignment)
• Add new examples in Section 9.7.2 (Metadata Encoding)

Example Use Cases

• Sentinel-2 data in UTM zones
• MODIS data in sinusoidal projection
• Polar research data in stereographic projections
• Regional datasets in local coordinate systems

cc @vincentsarago, @maxrjones, @briannapagan