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.