Encode geometries Google polyencoder style
Python Makefile
Fetching latest commit…
Cannot retrieve the latest commit at this time.
Permalink
Failed to load latest commit information.
polyencoder
tests
.gitignore
.travis.yml
LICENSE
Makefile
README.md
setup.cfg
setup.py

README.md

Polyencoder

Python module for Google Maps polyline encoding. Want your list of coordinates to look like e{~vF|c_ci|BqCI}Eyw@? You've come to the right place!

Includes command line utils for encoding a list of points or an entire geodata file.

Installing

Two options:

pip install polyencoder
pip install polyencoder[layer]

The first installs the basic polyencoder. The second installs Fiona, a dependencies for the layer encoder.

Requirements:

  • Python >= 2.7
  • GDAL (layer encoder only)

Command line

Encode a set of points:

polyencode point x0,y0 x1,y1

Encode a geodata layer (*.geojson, *.shp, etc):

polyencode layer id infile.geojson

This will produce tab-separated output:

1   e%7B%7EvF
2   kF%60%40wFDYtIea
3   ...

(Assuming that the 'id' field of the input is 1, 2, 3.)

You can specify more than one key with a comma:

polyencode layer id,name infile.geojson

By default, results are url-encoded. Get the raw result with --no-encode:

polyencode layer --no-encode id infile.geojson 

1   e{~vF|c_cMi|BqCg
2   AH~FmClIiLfEkR`AgOjCiOLYrF

By default, the result is tab-separated. Use another character:

polyencode layer --delimiter , id infile.geojson

API

>>> import polyencoder
>>> encoder = polyencoder.PolyEncoder()
# points are a sequence of (longitude,latitude) coordinate pairs
>>> points = ((8.94328,52.29834), (8.93614,52.29767), (8.93301,52.29322), (8.93036,52.28938), (8.97475,52.27014),)
>>> encoder.polyencode(points)
'soe~Hovqu@dCrk@xZpR~VpOfwBmtG'

The constructor takes several arguments:

  • num_levels specifies how many different levels of magnification the polyline will have. (default: 18)
  • zoom_factor specifies the change in magnification between those levels. (default: 2)
  • threshold indicates the length of a barely visible object at the highest zoom level. (default: 0.00001)
  • force_endpoints indicates whether or not the endpoints should be visible at all zoom levels. (default: True)

See http://facstaff.unca.edu/mcmcclur/GoogleMaps/EncodePolyline/description.html for more details on what these parameters mean and how to tweak them. The defaults are sensible for most situations.

License

This module is distributed under a BSD license.

The underlying polyencoder is is Python port of the Javascript Google Maps polyline encoder from Mark McClure, released under a BSD license. It is:

Copyright (c) 2009, Koordinates Limited
All rights reserved.

Updates and command line utils are

Copyright (c) 2015, Neil Freeman
All rights reserved.