sridentify is a command-line utility and Python API for quickly
identifying the EPSG Registry Code
from a .prj file typically associated with ESRI
Shapefiles. It ships with an
SQLite database containing mappings of Well-known
Text strings to EPSG
codes, the bulk of which was manually sourced and cleaned from an ESRI
website.
It's not complete, however, and in the event you test it against a WKT
string not in the database it can optionally search the
prj2epsg.org API. If the API returns an exact
match, that code is returned and saved to the SQLite database. Handling
several partial matches is currently planned, but not yet implemented. This feature can be disabled with the -n or --no-remote-api flags when running sridentify on the command line, or by instantiating with call_remote_api=False when using the Python API.
sridentify is written in Python, 2- and 3-compatible, and has no external dependencies.
Linux, OS X, other *nixes
pip install --user sridentify
The --user is important if installing system-wide (i.e., not in a virtualenv), because the
user running sridentify must have write permissions on the SQLite database in the event that
sridentify tries to save a new result fetched from the prj2epsg API to the database.
On most Linux systems pip install --user will install to $HOME/.local and place the executable script
in $HOME/.local/bin. You should add this to your $PATH if you want to run sridentify
without having to specify the full location to the executable. On OS X pip install --user should install it to somewhere already in your $PATH, but this may depend on how Python and/or pip was installed.
Anaconda is your best bet for installing sridentify on Windows. Assuming you have installed Anaconda, then launching an Anaconda prompt (should be available in the Start menu under Anaconda) and running pip install sridentify should work and make the sridentify executable available on your %PATH%. If you don't want to or cannot use Anaconda you should also be able to build and install sridentify systemwide or in any virtual environment with setuptools.
usage: sridentify [-h] [-n] prj
Identify an EPSG code from a .prj file
positional arguments:
prj The .prj file
optional arguments:
-h, --help show this help message and exit
-n, --no-remote-api Do not call the prj2epsg.org API if no match found in
the database
Get the EPSG code from a .prj file
$ sridentify seattle_land_use.prj
2285Example use in conjunction with the shp2pgsql command-line utility that ships with PostGIS. Assuming you have a PostGIS-enabled database named seattle, and you have a shapefile called seattle_land_use that you want to import into that database but you're not sure what spatial projection the shapefile uses:
$ shp2pgsql -s $(sridentify seattle_land_use.prj) -g the_geom -ID seattle_land_use.shp | psql -d seattle
Do not call the prj2epsg.org API if no match found in the database (e.g., if running in a script or if the API is unresponsive):
$ sridentify --no-remote-api seattle_land_use.prj
Let's say you have a directory full of shapefiles of different projections that you want to bulk import into PostGIS. You could use sridentify -n in a script to skip calling the API for those that don't match anything in the database for speed's sake (and politeness of not hammering away at the free prj2epsg.org service!). For example:
#!/usr/bin/env bash
for p in $(find . -name "*.prj")
do
epsg="$(sridentify -n $p)"
if [[ ! -z "$epsg" ]]
then
shp2pgsql -s $epsg -g the_geom -ID "${p/prj/shp}" | psql -d my_db_name
else
# log the unmatched prjs to a file
echo "no EPSG code found for $p" >> bulk_import.log
fi
done>>> from sridentify import Sridentify
>>> # Read .prj file from the filesystem
>>> ident = Sridentify()
>>> ident.from_file('/path/to/seattle_land_use.prj')
>>> ident.get_epsg()
2285
>>> # Paste in Well-Known Text string directly
>>> ident = Sridentify(prj="""PROJCS["NAD_1983_StatePlane_Washington_North_FIPS_4601_Feet",GEOGCS["GCS_North_American_1983",DATUM["D_North_American_1983",SPHEROID["GRS_1980",6378137.0,298.257222101]],PRIMEM["Greenwich",0.0],UNIT["Degree",0.0174532925199433]],PROJECTION["Lambert_Conformal_Conic"],PARAMETER["False_Easting",1640416.666666667],PARAMETER["False_Northing",0.0],PARAMETER["Central_Meridian",-120.8333333333333],PARAMETER["Standard_Parallel_1",47.5],PARAMETER["Standard_Parallel_2",48.73333333333333],PARAMETER["Latitude_Of_Origin",47.0],UNIT["Foot_US",0.3048006096012192]]""")
>>> ident.get_epsg()
2285
>>> # Do not call the prj2epsg.org API if no match found
>>> ident = Sridentify(call_remote_api=False)
>>> ident.from_file('foo.prj')
>>> ident.get_epsg() # would return None
>>>
>>> # Instantiate with strict=False to log errors and return None
>>> # instead of raising Exceptions when trying to read in problematic files.
>>> ident = Sridentify(strict=False)
>>> # example: accidentally trying to read in a binary file
>>> ident.from_file('seattle_land_use.shp') # this would log an error message
>>> ident.get_epsg() # would return None
>>> ident = Sridentify(strict=True) # the default
>>> ident.from_file('seattle_land_use.shp')
>>> # Will raise UnicodeDecodeError: 'utf-8' codec can't decode byte 0x88 in position 10: invalid start byte
>>> # Write out a WKT string in the database to a file
>>> ident = Sridentify()
>>> ident.from_epsg(4269)
>>> ident.to_prj('/path/to/4269.prj')More and more governments and organizations are making their GIS data available to the public on open data portals. Local governments typically store and use GIS data in the map projection most appropriate for their location on planet Earth. For the United States, this is typically the State Plane Coordinate System. Other common systems are Universal Transverse Mercator, or a highly localized system that is accurate only within the geographic boundaries of the entity's jusrisdiction.
ESRI Shapefiles are a common format for publishing GIS data, although a "shapefile" with the .shp extension is really just data describing the geometry. Shapefiles are typically bundled with a dBase file ( .dbf extension ) which contains data attributes about the geometry and a small text file describing the spatial reference system of the geomtry in WKT format.
sridentify is not meant to be a full-fledged client library to the actual
EPSG database. If that's what you need, you're probably looking for something like python-epsg.
Rather, sridentify is for those looking to quickly identify the EPSG code
of a shapefile, especially when importing into PostGIS. Of course, you could use ogr2ogr
to convert everything into a web-friendly projection, like:
$ ogr2ogr -f PostgreSQL -t_srs EPSG:4326 PG:dbname=seattle seattle_land_use.shpBut transforming spatial data from one projection to another is a lossy operation and can result in coordinate drift. Ideally, you would store the original data in its original coordinate system and then transform copies as needed.