Defence Geospatial Information Working Group (DGIWG) P5: Geospatial Web Services Program Proposed Extension for Multi-resolution Vector Data in OGC GeoPackage May 12, 2016

Defense Geospatial Information Working Group (DGIWG) 12-May-2016 Background In May 2015, DGIWG sent out a questionnaire to member nations to prioritize possible GeoPackage extensions from a military perspective. The result of this questionnaire was presented at the OGC meeting in Boulder, June Efficient handling of multi-resolution vector data was identified as one of three high-priority extensions (along with symbology and handling of coverage data).

Defense Geospatial Information Working Group (DGIWG) 12-May-2016 Rationale for the Proposed Extension Today’s support for vector data in OGC GeoPackages does not provide enough support for reading and displaying large geospatial datasets in applications. Using a spatial index (GeoPackage Extension RTree Spatial Indexes, gpkg_rtree_index) improves performance when reading the data at zoomed in levels, but it does not help if you zoom out. When using large datasets, zooming out far enough in an application can cause it to read so much data that it becomes unusable (or even crashes). Even if the application applies some filtering to reduce the amount of data that is displayed at zoomed-out levels, each geospatial object still has to be accessed, if only by SQLite.

Defense Geospatial Information Working Group (DGIWG) 12-May-2016 Two Possible Solutions 1.Introduce a “tiled vector pyramid” concept – similar to the existing tiled raster pyramids. – Work is ongoing in OGC OWS-12 to investigate this approach. 2.Add a new metadata table to describe tables that logically contain the same data but for different scale intervals. – This is the solution that is proposed by DGIWG in this presentation.

Defense Geospatial Information Working Group (DGIWG) 12-May-2016 “Tiled Vector Pyramids” – pros and cons Adding support for tiled vector pyramids – similar to tiled raster pyramids – might provide a solution for this problem. Pros: – Large datasets can be read efficiently without requiring the reader to support the gpkg_rtree_index extension. – Provides an opportunity to specify a new binary format for vector tiles that could reduce the size of the data on disk. Cons: – Requires a new binary format for vector tiles. – Extensive effort to specify and implement means that it could take long until clients, production tools and data are available. – Only clients that support the new format will be able to access the data.

Defense Geospatial Information Working Group (DGIWG) 12-May-2016 DGIWG Proposed Solution Add a new metadata table to OGC GeoPackage to describe tables that logically contain the same data but for different scale intervals. Applications can inspect this metadata table at runtime to determine which tables are suitable to use at which scale intervals. The format of the new metadata table could be specified in a new GeoPackage extension.

Defense Geospatial Information Working Group (DGIWG) 12-May-2016 Proposed Solution – pros and cons Pros: – All vector tables are still regular vector tables – readable by any OGC GeoPackage compliant reader in the same way as before. – Easy to implement: – Individual vector tables are read in the same way as before and only minor changes are necessary to make applications switch between tables at different scales. – Production tools need to be updated to write to the new metadata tables. The vector data is written in the same way as before. Cons: – Some data will be duplicated in multiple tables, but usually at a lower level of detail and therefore using less space than the most detailed version.

Defense Geospatial Information Working Group (DGIWG) 12-May-2016 Proposed Solution – Draft Table Structure