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in reply to Geo Package files

You can use Geo::GDAL::FFI to read the contents of a geopackage (untested example code below). The geometry field is stored as Well Known Binary (WKB), or perhaps a variant of it. This can be converted to Well Known Text (WKT) to be human readable.

A definition of WKB is given in the libgeos docs at https://libgeos.org/specifications/wkb, and WKT at https://libgeos.org/specifications/wkt/.

The GDAL stack can be a beast to install if the aliens have to compile everything from source (GDAL, Proj, GEOS, libtiff, libsqlite3, optionally also spatialite, freexl and curl). If you are on a unix type machine then install the gdal-dev package using your system package manager, then the GDAL aliens will run system installs.

Example code:

#  adapted from the Geo::GDAL::FFI docs, untested
my $layer_name = 'some_layer';
my $db = Open('test.gpkg');
my $layer = $dataset->GetLayer($layer_name);
$layer->ResetReading;
while (my $feature = $layer->GetNextFeature) {
    my $value = $feature->GetField('name');
    my $geom = $feature->GetGeomField;
    say $value, ' ', $geom->AsText;
}

[download]

Update: More details of the geopackage geometry format are at http://www.geopackage.org/spec131/index.html#gpb_format. This should be of use if you decide to write your own parser to extract the first and last coordinates of each linestring.

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Re^2: Geo Package files
by Bod (Parson) on Mar 04, 2022 at 00:57 UTC

    Alas I am on Windows and the way to install GDAL seems to be via Anaconda.

    If I can suss out the correct template for unpack then I shall do it that way. But if that proves impossible, or at least too tricky for me, then I'll come back to GDAL.

    The WKB link is certainly helpful, thanks.

[reply]

      You could have a look at the GIS Internals stable releases. They provide precompiled binaries for windows with a broad range of dependencies (including almost all those I listed in my previous post). If the GIS Internals paths can be found by the various gdal-stack aliens then they will run system installs.

      Edit: Be sure to also get the download flagged as "compiled libraries and headers"

      Another edit: I just tested with the GIS Internals files and the alienfile probe for geos does not work (the probe currently uses geos-config, which is not included).

[reply]

      Rather than try and get things to work on the inferior OS you might find it worth the effort (to say nothing of being less headaches) to install a docker host and see if you can't get a dedicated environment running a decent real OS instead. With that available then you could install the more off-the-shelf tool chain into it more easily (theoretically . . .). Instead of trying to jump through all these hoops getting this (as you say elsewhere in the thread) occasional procedure running "native" you can just spin up a container to process the results and dump the output out as you need it into a shared volume that you then work with from your "normal" platform.

      Edit: Looks like there's an osgeo/gdal available which you probably could build upon.

      The cake is a lie.
      The cake is a lie.
      The cake is a lie.

[reply]

        As I've reached the point I've got to, my gut feeling is that it is worth continuing. Perhaps not for this project, but certainly for what I am learning in the process of doing this. Previously, the only use I've made of unpack is to split up an authentication string.

        I think knowing more about pack and unpack would be beneficial to me. Thanks to soonix and Marshall my understanding of these two functions in improving. That alone makes continuing worthwhile.

[reply]

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