Hey Jukka,
Although it uses SQLlite, it sounds like GeoPackage is a data storage
mechanism like shapefiles, more than a general queryable data store. For
that reason, it's probably a better fit in OJ as one of the options for
"Open", "Open File...". That said, it would probably be fun to work on,
and I'll put that on my todo list unless someone else wants to take it.
But first I need to get that patch for the JTS WKBReader....
-lreeder
On Tue, Dec 3, 2013 at 1:56 AM, Rahkonen Jukka <jukka.rahko...@mmmtike.fi>wrote:
> Hi,
>
> I started a new thread because Larry Reeder wrote " Now that cold is here,
> I've got more time to stay indoors and code. "
> I have a feeling that if it will be cold enough then Larry can make the
> plugin to read aldo blobs from GeoPackage databases.
>
> GeoPackage is a new OGC Standard candidate. Info about that is in
> https://github.com/opengis/geopackage
> and the version 0.8 is available from
> https://portal.opengeospatial.org/files/?artifact_id=54838
>
> When it comes to DB Query plugin, the GeoPackage is a SQLite database
> where geometries have been stored as BLOBs. These BLOBs contain standard
> WKB presentation with some headers. The binary format is described here
> http://opengis.github.io/geopackage/#gpb_format
>
> Unfortunately I could not find any public GeoPackage database sample but
> such can be downloaded after registration from Luciad
> http://demo.luciad.com/GeoPackage/Download.html
> Luciad has also started on open source project for a geopackage library
> https://bitbucket.org/luciad/libgpkg/overview
> There seems to be also some GeoTools code for GeoPackages but I am not
> sure if it is up to date. The binary format was changed a bit perhaps in
> August.
> http://docs.geotools.org/latest/javadocs/org/geotools/geopkg/GeoPackage.html
>
> What DB Query tool should do is to read the BLOB, interpret the headers
> and jump to correct byte offset for reading the WKB so that it can be
> passed on to JTS. I tried to read some older version of the specification
> version in July, 2013 and came the this conclusion:
>
> 1) Check if BLOB begins with "GPB" bytes (47 50 42). If yes, then it is a
> GeoPagkage BLOB.
> 2) Study the fourth byte and find the envelope type from "E" bits (1, 2,
> and 3).
> 3) Skip the four srs_id bytes and based on the envelope type, either 0,
> 32, 48, or 64 bytes more.
> 4) Here starts the WKB
>
> Thus the first byte of WKB is either byte number 9, 41, 57, or 73.
>
> I am not sure if this was a perfect interpretation ever of if adjustments
> to the spec has changed things but I believe that logically this is close
> to correct.
>
> -Jukka Rahkonen-
>
>
>
>
>
>
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