Question

I am building a system which lets users upload shapefiles. It then converts those shapefiles to PostGIS using shp2pgsql. This command requires the SRS ID in form of an EPSG code.

So I need a ruby gem that can read the shapefile’s *.prj file (which contains the projection/spatial reference system encoded as WKT) and return a corresponding SRS ID.

Answer 1

I’m not sure how Ruby bindings work to GDAL, but OSR (part of GDAL) can extract either the projection WKT (text) or the SRID (integer).

See this gis.SE answer for a solution with Python/GDAL/OSR.

Update: It turns out the Ruby bindings work nicely as expected. To get you going, try this code:

require 'gdal/osr'

prj_fname = 'myfile.prj'
prj = File.open( prj_fname )

# Import the WKT from the PRJ file
srs = Gdal::Osr::SpatialReference.new()
srs.import_from_wkt( prj.read )

# Various exports
puts srs.export_to_wkt

srs.auto_identify_epsg
puts srs.get_authority_name(nil)
puts srs.get_authority_code(nil)

If you need some other aspect of the projection, explore the available public methods:

srs.public_methods.sort