Le mardi 18 octobre 2016 12:13:59, Rahkonen Jukka (MML) a écrit :
> Hi,
> >Given that the modules are unsupported and not working properly anyways,
> >I'd >rather fix things to follow GDAL's approach. Any objection?
> No objection. If two open source GIS software under the OSGeo umbrella do
> something in the same way we can start calling it as a de facto standard.

In the matter that would be more like "profiles" of what is allowed within the 
OGC standard.

> Even has been committing a lot to GPKG lately but mostly to the vector
> side. It might still be good to check if GDAL still follows the same
> approach as you are planning to follow.

No change in the GPKG raster approach on the GDAL side done recently. Andrea's 
analysis matches well how it is designed.

Note that Brad Hards identified a possible non compliance of the GDAL writer in 
some circumstances regarding a picky requirement
See (the part about Requirement 45, the issue with now vs CURRENT_TIMESTAMP 
has now been fixed)

> -Jukka Rahkonen-
> Andrea Aime wrote:
> [Geoserver-devel] Geopackage tiles generation issues
> Hi,
> I am looking into why the raster geopackages GeoServer generates via the
> geopackage module are not being read correctly by gdal and found a few
> issues, some straight bugs, other more like odd design decisions.
> The straight bug is what's causing GDAL not to read the files correctly,
> the current code, shared with mbtiles generation, forces the request to be
> cast on a GWC managed gridset (and actually works only if the requested
> layers are cached, which is a bit of a nonsense to me given this is a WMS
> request...), and uses that gridset coordinates for tiles.
> Now the problem is that in the geopackage metadata for the layer and the
> gridset we are declaring the requested bbox, not the ones used for tiles
> generation, resulting in tile coordinates being off the expected grid.
> Now, geopackage natively has the layer bounds that are separate from the
> tile matrix ones, but the current geotools code forces them to be the
> same.. that's a limitation I'm fixing.
> However, the main issue remains... if someone asks for a layer in a certain
> SRS, why try to coax it into a tile matrix managed by GWC?
> I believe the intention was to try and leverage GWC cache, but still, while
> I understand taking the opportunity if possible, in my opinion the request
> of the user should be respected, and if the request is not a match either
> by SRS or BBOX to a tileset, GeoServer should not force a different
> response.
> From the same line of thought, a WMS request should not fail if it's made
> against a layer that is not cached by GWC, like it does today, with a
> strange error message too, e.g. asking for UTM 32N, which is not tile
> cached:
> http://demo.geo-solutions.it/geoserver/wms/reflect?layers=nurc:mosaic&srs=E
> PSG:32632&format=geopackage
> results in:
> java.lang.IllegalArgumentException: Thread 19276 Unknown layer nurc:mosaic.
> Check the logfiles, it may not have loaded properly
> The second thing that I find confusing is, if I asked for a result image
> that's 768 pixels wide, why am I getting back a geopackage that's over
> 100000 pixels wide? That's... insane, especially for a WMS request (large
> jobs should be deferred to WPS asynch requests). Looking at the code,
> there is logic that generates the min and max zoom levels for the tile
> matrix, and it does something rather surprising... it picks the zoom level
> closest to the requested one as the min zoom level, and then starts adding
> zoom levels until the matrix has (stricly) more than 256 tiles in width...
> in my case, that means 512 tiles, or a total width of 512*256=131072
> pixels!
> Trying GDAL on the command line, translating from a geotiff to a
> geopackage, it makes what looks like a more sensible choice instead: it
> uses the requested zoom level as the _maximum_ one, and then adds
> overviews to it, in the cases I've tried, until a single tile is left
> (basically, a good output with overviews). With our case we can also
> generate raster geopackages out of vector layers, and creating the
> overviews might end up hitting badly setup styles displaying too much
> data, but still, that would be a problem also in random WMS requests, so
> I'm not too concerned...
> Also, by default, GDAL generates a gridset that's an exact match for the
> source data, meaning a custom one. That also makes sense to me, if someone
> wants something other than the BBOX/SRS requested there are format options
> to choose both the target gridset and min/max zoom levels.
> Given that the modules are unsupported and not working properly anyways,
> I'd rather fix things to follow GDAL's approach. Any objection?
> Cheers
> Andrea
> --
> ==
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> ==
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