Add Triangle and Hex Grid Encoding for GeoGridAggregator

[nknize]

A triangular tessellation based geo_point encoding supports aggregating on grids other than basic geohash (e.g., triangular, hex). These aggregations provide better spatial visualization but are also commonly used in GIS analysis applications due to their equal area characteristics. This feature issue adds a grid_type parameter to GeoHashGridParams (which will likely need to be refactored to GeoGridParams) to allow users to specify different grid types such as geohash, triangular, hexagonal. We should also investigate generalizing geohash_grid aggregation to a more general geo_grid aggregation so we can provide different grid definitions.

[djminkus]

Is a solution for this still desired?

[thomasneirynck]

Would this include also quad_keys, similar to Bing Maps (https://msdn.microsoft.com/en-us/library/bb259689.aspx)?

The tile-pyramids employed by most mapping services (Web Mercator, 2x2 division) are easier to work with from a front-end perspective than geohash-grids due to the uniform scaling horizontal/vertical across zoom levels.

So something like https://www.elastic.co/guide/en/elasticsearch/reference/current/search-aggregations-bucket-geohashgrid-aggregation.html, but bucketing by tile in the quad-tree.

[jpountz]

FWIW I got a user asking for this to me in person recently, the main motivation being to have equally-sized cells.

[DaveCTurner]

Relates #28121 - S2's cells are approximately rectangular and of approximately equal sizes.

[nyurik]

I just submitted a pull request #30231 with plus code support - I think that PR can be used as a step towards multi-hashing support.

[consulthys]

It would definitely be a good idea to support hexagonal partitioning.
See Uber's open-sourced h3 project (Hexagonal Hierarchical Geospatial Indexing System): https://github.com/uber/h3

Explanations with examples here: https://eng.uber.com/h3/