[Geopackage] Tile gridded elevation data: compulsories entries in gpkg_2d_gridded_coverage_ancillary and gpkg_2d_gridded_tile_ancillary ?

Even Rouault even.rouault at spatialys.com
Wed Mar 1 09:48:33 EST 2017


Hi,

If I read http://www.geopackage.org/spec/#extension_tiled_gridded_elevation_data
in a pedantic way, 

* there's no requirement to insert a new row in gpkg_2d_gridded_coverage_ancillary each
time you have a row in gpkg_contents with datatype = '2d-gridded-coverage' . I guess we at least
need such a row to know if it is a 'integer' or 'float' coverage, but I'm not so sure as there are
sensible default values in the DDL, so it could be assumed to be a coverage of type integer,
with scale = 1, offset = 0, precision = 1 and n nodata.

My current implementation in GDAL would reject such a lack of row in gpkg_2d_gridded_coverage_ancillary

* there's no requirement to inset a new row in gpkg_2d_gridded_tile_ancillary for each tile
of the tile pyramid user data table. And that could make sense to not fill it if the data is of type
'float' or if scale = 1 and offset = 0.

My current implementation in GDAL will accept such missing rows on reading (and assume
tile scale = 1 and tile offset = 0), but will always write them.

Any thoughs about the above: lack of requirements, or are missing rows acceptable ?

Thanks,

Even

-- 
Spatialys - Geospatial professional services
http://www.spatialys.com
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