Fast Polylines

Gem GitHub Workflow Status

Implementation of the Google polyline algorithm.

BREAKING CHANGES: The version 2 of FastPolylines includes breaking changes, see Migrate from V1

About 300x faster encoding and decoding than Joshua Clayton's gem.

make benchmark on a MacBook pro 13 - 2,3 GHz Intel Core i5:

——————————————————————————————— ENCODING ————————————————————————————————

Warming up --------------------------------------
           Polylines   310.000  i/100ms
     FastPolylinesV1     2.607k i/100ms
     FastPolylinesV2    59.833k i/100ms
Calculating -------------------------------------
           Polylines      2.957k (± 5.9%) i/s -     14.880k in   5.049867s
     FastPolylinesV1     25.644k (± 5.8%) i/s -    127.743k in   4.999954s
     FastPolylinesV2    682.981k (± 7.7%) i/s -      3.410M in   5.025952s

     FastPolylinesV2:   682980.7 i/s
     FastPolylinesV1:    25643.7 i/s - 26.63x  slower
           Polylines:     2957.1 i/s - 230.97x  slower

———————————————————————————————  DECODING ————————————————————————————————

Warming up --------------------------------------
           Polylines   127.000  i/100ms
     FastPolylinesV1     1.225k i/100ms
     FastPolylinesV2    40.667k i/100ms
Calculating -------------------------------------
           Polylines      1.289k (± 6.1%) i/s -      6.477k in   5.046552s
     FastPolylinesV1     15.445k (± 4.4%) i/s -     77.175k in   5.006896s
     FastPolylinesV2    468.413k (± 7.8%) i/s -      2.359M in   5.068936s

     FastPolylinesV2:   468412.8 i/s
     FastPolylinesV1:    15445.4 i/s - 30.33x  slower
           Polylines:     1288.8 i/s - 363.46x  slower


gem install fast-polylines

or in your Gemfile:

gem "fast-polylines", "~> 2.0.0"


require "fast_polylines"

FastPolylines.encode([[38.5, -120.2], [40.7, -120.95], [43.252, -126.453]])
# "_p~iF~ps|U_ulLnnqC_mqNvxq`@"

# [[38.5, -120.2], [40.7, -120.95], [43.252, -126.453]]

Advanced usage

Use a different precision

Default precision is 5 decimals, to use a precision of 6:

FastPolylines.encode([[38.5, -120.2], [40.7, -120.95], [43.252, -126.453]], 6)
# "_izlhA~rlgdF_{[email protected]_kwzCn`{nI"

FastPolylines.decode("_izlhA~rlgdF_{[email protected]_kwzCn`{nI", 6)
# [[38.5, -120.2], [40.7, -120.95], [43.252, -126.453]]

The precision max is 13.

Migrate from V1


# before
require "fast-polylines"
FastPolylines::Encoder.encode([[1.2, 1.2], [2.4, 2.4]], 1e6)
# after
require "fast_polylines"
FastPolylines.encode([[1.2, 1.2], [2.4, 2.4]], 6)


The new version of FastPolylines doesn't support precision more than 1e13, you should not consider using it anyway since it is way too precise.

Encoder and Decoder modules are deprecated in favor of the single parent module. Even though you can still use those, a deprecation warning will be printed.

The precision is now an integer representing the number of decimals. It is slightly smaller, and mostly this will avoid having any float value as precision.

The file name to require is now snake_cased, you'll have to require fast_polylines. The gem name stays the same however.

Run the Benchmark

You can run the benchmark with make benchmark.


git clone [email protected]:klaxit/fast-polylines
cd fast-polylines
bundle install
# Implement a feature, resolve a bug...
make rubocop
make test
git commit "My new feature!"
# Make a PR

There is a make console command as well to open a ruby console with the current version loaded.

And here's a good starting point for Ruby C extensions knowledge.


Please see LICENSE