Remove unneeded columns from geographic data file?

Question

I have some GML data that has some unneeded columns in it. I'd like to remove these columns in order to reduce the file size. (To clarify: I mean that the file has many points in it, and each of these points has some metadata attached, and I don't need all of the metadata.)

I'd also like to do this from the command line, as I have many files.

I can convert the GML files into different formats using ogr2ogr, so my question is this: what's the easiest way to remove a column from a geographic data file, from the command line?

I'm a Python programmer so my instinct would be to convert the file to GeoJSON, then use Python's JSON-parsing methods to read and rewrite the JSON file.

But perhaps there's a more direct way, using a GDAL tool or similar.

Answer 1

Shapefile as a temporary file format is not necessary and it may also alter the GML data (shorten attribute names, cut strings to max 255 characters, change DATETIME to DATE etc.)

I would use ogr2ogr not by dropping unwanted attributes but by selecting those which are wanted. The SQLite SQL dialect is more standard than the defauld OGR dialect, that's why I use that even it is not necessary for this query.

ogr2ogr -f GML -dialect SQLite -sql "SELECT attr1, attr2, attr3,... FROM layer" output.gml input.gml

Answer 2

You can delete a field using OGR SQL and choosing an OGR format which supports the field deletion. Unfortunately GML doesn't support it, so you have to pass through another format, e.g. SHP:

ogr2ogr temp.shp input.gml
ogrinfo temp.shp -sql "ALTER TABLE temp DROP COLUMN field_to_drop"
ogr2ogr -f GML output.gml temp.shp