Tracking bug for `kart export` command (vector / table)

[olsen232]

kart import lets you take a non-Kart dataset and import it to Kart.
There's no opposite command that takes a Kart dataset and exports it as some non-kart dataset type.

(Except that, if you really need to, you can use the working-copy creation functionality to export a dataset, or, use ogr2ogr on the contents of your working copy, or use ogr2ogr plus the experimental OGR driver in checked into contrib/.

This is the tracking bug for adding a kart export command. It will use GDAL OGR drivers internally and so will immediately support export to most anything that OGR supports, and it will feel familiar for anyone used to using ogr2ogr.

A downside to this approach is that we might have a bit more OGR behaviour / bugs than we want, until and unless we special case them or work around them. For example:

• Connection strings for postgres / MSSQL drivers will have to be in the format that OGR expects, not the format that Kart expects.
• OGR's type system doesn't have NUMERIC as a separate type from INTEGER / FLOAT, so handling of these types tends to be a bit inconsistent - this is one reason that kart import mostly doesn't use OGR any more.

(This issue is just for vector + tabular datasets - kart export for raster or point cloud datasets will need a separate command to be written. Using the working copy contents + gdal_translate or pdal translate works okay for exporting those formats in the meantime)

[olsen232]

Implemented in the following PRs:
#988
#990
#991

[olsen232]

Mostly done except I should update the docs at https://docs.kartproject.org/en/latest/pages/command_reference.html

Possible future enhancements:

• export for raster and point clouds
• export lots of things at once eg kart export --all-tables
• prevent the user (or at least warn them against) exporting data into the working copy that kart is already maintaining

[craigds]

I've experimented a bit with this and had a few issues/suggestions:

• kart export --help shows no options (you have to kart table-export --help). why are there two since it only supports tables anyway?
• need a way to select an export format - it seems to auto-detect based on file extension, but no way to override
• VSI URLs work as an export dest 🎉 but would work better if we set CPL_VSIL_USE_TEMP_FILE_FOR_RANDOM_WRITE=YES (GDAL tells you this if you try to export to a /vsis3/bucketname/file.fgb)
• should support - as an easy way of exporting to stdout (for streamable export formats anyway) - just wrap /vsistdout/

[olsen232]

why are there two since it only supports tables anyway?

We might one day support raster or point cloud export, so I've reserved space for this possibility so that we don't have to move things around later
kart table-export export tables
kart raster-export exports rasters...
...
kart export forwards to the appropriate command, where it can be inferred, and shows a --help that has options common to all subcommands

However it's true that in the meantime we may as well just alias the one to the other so that it shows the kart table-export help page.

[olsen232]

need a way to select an export format - it seems to auto-detect based on file extension, but no way to override

This isn't well documented but kart export --help says the command format is:
kart export [OPTIONS] DATASET [EXPORT_TYPE:]DESTINATION

so, for example, GPKG:output.db would work. But yes this should be clarified