On lundi 29 janvier 2018 10:21:04 CET Stefan Keller wrote: > Hi Even > > Great news about this MVT reader! > > The docs [1] says: > > The MVT driver only uses the "json" key to retrieve the layer names, their > > fields and the geometry type, and the "bounds" key for the layer extent. > I just wanted to point you to the spec. discussion of MBTiles and > TileJSON metadata [2] and I hope the SW keeps aligned with it.
Yeah, I didn't really found a specification for those. Just my experiments with various MBTiles / directory of tiles found in the wild, and those I produced with tippecanoe. > > > If this file cannot be found, the layer schema is established by scanning > > the features of the tile(s). > Q1: So the reader scans all tiles on the one given zoom level and > generates an internal metadata structure for that zoom level? Yes. Potentially with a limitation on the number of tiles to explore with the TILE_COUNT_TO_ESTABLISH_FEATURE_DEFN open option > Q2: Option JSON_FIELD=YES says "put all attributes as a serialized > JSon dictionary"; Can a metadata.json file also be written to disk in > case it was generated? Not sure to understand your question. If you use JSON_FIELD=YES, it means that the driver will not try to establish a full schema that fit for all features, but just put the key/value pair it finds for each feature in a JSon dictionnary. So there's no metadata.json to write. > Q3: Is this metadata.json accessible from an GDAL/OGR Python binding? The open option you mean ? Yes: https://github.com/OSGeo/gdal/blob/trunk/autotest/ogr/ogr_mvt.py#L69 > Q4: Ultimately I'd like to get a metadata.json (TileJSON compatible) > from the above mentioned MVT input for all zoom levels (at least for > the json key): How could I achieve this? Manually. By iterating on the OGR layer feature definition. Are there use cases where metadata.json is missing ? Note: I'm going to work on the write side of the drivers in the coming weeks. Even -- Spatialys - Geospatial professional services http://www.spatialys.com
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