encoded_polyline's Introduction

EncodedPolyline

EncodedPolyline implements Google's algorithm for compressing arrays of geographic points. The compressed string can then be passed to the Google Maps API. The Maps API limits URL requests to 2048 characters. This library does not enforce this limit on the encoding length. This coordinate encoding scheme is also compatible with MapQuest Platform Services, which supports variable decimal precision. The default precision of 5 is appropriate for compatibility with the Google Maps API.

Installation

gem install encoded_polyline

Examples

Using the library with default decimal precision of 5:

EncodedPolyline.encode(-179.9832104)                  # "`~oia@"
EncodedPolyline.decode("`~oia@")                      # -179.98321
EncodedPolyline.encode_points([[37.782,-122.406]])    # "ohreFnlbjV"
EncodedPolyline.decode_points("ohreFnlbjV")           # [[37.782,-122.406]]

Using the library with explicit decimal precisions:

EncodedPolyline.encode(-179.9832104, 7)               # "na`|gjB"
EncodedPolyline.decode("na`|gjB", 7)                  # -179.9832104
EncodedPolyline.encode_points([[37.782,-122.406]], 2) # "ckF`|V"
EncodedPolyline.decode_points("ckF`|V", 2)            # [[37.78, -122.41]]

It is important to specify the same precision when encoding and decoding. Otherwise, decoded coordinates may be wrong by orders of magnitude.

Performance

Included is a benchmark that creates a 100-point random walk, gives you a URL, and encodes/decodes it 10,000 times (1 million points total).

Raw length(JSON):     3682 characters
Encoded length:       495 characters
Compression ratio:    0.134437805540467

                          user     system      total        real
encoding              9.090000   0.000000   9.090000 (  9.092519)
decoding             16.470000   0.010000  16.480000 ( 16.473547)

Contributors

bdon - author

anoved - explicit precision, MapQuest support

Copyright

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