OGC RBT Sprint Follow-up 1

OGC has recently completed the Releasable Basemap Tiles Sprint. From my perspective as the GeoPackage Standards Working Group Chair, the goals of this code sprint were the following:

• Demonstrate the viability and interoperability of raster and vector map tiles in a GeoPackage;
• Exercise and review the existing specifications and draft standards for tiled feature data and styling and symbology that have been under development since at least 2019; and
• Prepare draft standards for public review and hopefully OGC adoption.

The sprint looked at three emerging standards: tiled feature data, semantic annotations, and styling and symbology. We will focus on tiled feature data here. As described in my previous post, the goal is to store feature data in a more efficient manner by leveraging the existing tiles option. This approach builds on the one devised by Mapbox in their Vector Tiles, but without being tethered to it. Mapbox Vector Tiles is Mapbox's intellectual property and the OGC community has asked for an alternative that offers more flexibility.

The approach that is in progress now and should be released soon for public comment will have  a set of conformance classes in a single document. From a governance perspective, the conformance classes allow implementers to implement as much or as little as they see fit. From a GeoPackage perspective, the conformance classes will appear as rows to the gpkg_extensions table, to make them discoverable by clients. Following are the planned conformance classes:

1. Base, establishing the gpkgext_vt_layers and gpkgext_vt_fields tables that govern what layers and what fields are in what tile sets.
2. Mapbox Vector Tiles, indicating that individual tiles are encoded using Mapbox's protocol buffers-based encoding.
3. GeoJSON, indiating that individual tiles are encoded as a GeoJSON file.
4. WKB Collection, indicating that the individual tiles are encoded as collections of Well Known Binary BLOBs. This is a relatively new option that could obviate the need for the GeoJSON option.
5. Attributes, indicating that feature attribution will be stored separately from the tiles themselves, using the GeoPackage Attributes Option.
6. Features / Tiles Mapping, indicating that the GeoPackage Related Tables Extension will be used to track the many-to-many relationship between tiles and features, potentially improving efficiency and adding improved querying options.