Google's Encoded Polyline Algorithm (Python)

2.0.4 · active · verified Sat Apr 11

The `polyline` library is a Python implementation of Google's Encoded Polyline Algorithm Format. It provides functionality to encode a list of latitude/longitude coordinates into a compact polyline string and to decode such a string back into coordinates. The library is actively maintained, with the current stable version being 2.0.4, and is released on an as-needed basis for bug fixes and feature enhancements.

Warnings

breaking Version 2.0.0 and above of `polyline` only supports Python 3.7+. For applications requiring Python 2 support, you must install version 1.4.0.
Fix: Upgrade to Python 3.7+ or pin the `polyline` library version to 1.4.0 (e.g., `pip install polyline==1.4.0`).
gotcha The `polyline` library uses `(latitude, longitude)` order by default for `encode` input and `decode` output, which is common in GIS but differs from the `(longitude, latitude)` order used in GeoJSON standards.
Fix: Use the `geojson=True` parameter in both `polyline.encode()` and `polyline.decode()` to work with `(longitude, latitude)` coordinate tuples.
gotcha The `precision` parameter (defaulting to 5) must be consistent between encoding and decoding operations to ensure accurate round-tripping of coordinates.
Fix: Explicitly set the `precision` parameter during both `encode` and `decode` if a non-default precision is desired or expected.
gotcha When loading polyline strings from external sources like CSV files, be mindful of backslash escaping. Python's CSV reader or other parsing mechanisms might interpret `\` differently, leading to corrupted polyline strings.
Fix: Ensure that backslashes in the polyline string are correctly escaped or unescaped during parsing. For example, if a `\\` in a CSV becomes `\` in Python, you might need `.replace('\\','\')` before decoding.

Install

pip install polyline Install stable version

Imports

encode
```
import polyline
polyline.encode(...)
```
The primary functions `encode` and `decode` are directly available under the `polyline` module namespace, not as classes.
decode
```
import polyline
polyline.decode(...)
```
The primary functions `encode` and `decode` are directly available under the `polyline` module namespace, not as classes.

Quickstart

This quickstart demonstrates encoding a list of `(latitude, longitude)` tuples into a polyline string and then decoding it back. It also shows how to handle GeoJSON-style `(longitude, latitude)` order using the `geojson=True` parameter and how to specify a custom precision.

import polyline

# Example coordinates: (latitude, longitude)
coords = [
    (38.5, -120.2),
    (40.7, -120.9),
    (43.2, -126.4)
]

# Encode coordinates into a polyline string with default precision (5)
encoded_polyline = polyline.encode(coords)
print(f"Encoded Polyline: {encoded_polyline}")

# Decode the polyline string back to coordinates
decoded_coords = polyline.decode(encoded_polyline)
print(f"Decoded Coordinates: {decoded_coords}")

# Example with GeoJSON style (lon, lat) and custom precision
geojson_coords = [
    (-120.2, 38.5),
    (-120.9, 40.7),
    (-126.4, 43.2)
]
encoded_geojson = polyline.encode(geojson_coords, precision=6, geojson=True)
print(f"Encoded GeoJSON Polyline (precision 6): {encoded_geojson}")
decoded_geojson = polyline.decode(encoded_geojson, precision=6, geojson=True)
print(f"Decoded GeoJSON Coordinates (precision 6): {decoded_geojson}")

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