Decoding Google Maps Encoded Polylines using PHP

2 August 2008

I’ve talked about the Google Maps encoded polyline format before. While there’s some nice utilities for encoding polylines that take the work out of implementing it yourself, I couldn’t find many polyline decoders.

This made it somewhat tedious to decode them, as the only way to get the original list of points was to create a GPolyline and then pull out the points from that object. This is not ideal since the work must always be done on the client side with JavaScript and using Google Maps.

To solve this, I quickly ported the algorithm over to PHP from the JavaScript source. Please feel free to download/modify/use this script.

Google Maps Polyline Decoder in PHP

Since the encoded polyline format offers numerous benefits (and because I had data already stored in this format) I did not want to move away from it. At the same time, I needed access to the points for working with things like Google Static Maps, which curiously does not accept the encoded polyline format for displaying paths. (Probably to reduce resource usage on their end, since decoding takes CPU time)

Thankfully the polyline decoding algorithm was already available at Mark McClure’s site. I spent a few minutes understanding the process and porting it over to PHP. The source is attached above and is released under an MIT license. Basically, the only change I had to make was to use some PHP functions to convert characters to their ASCII code, since PHP doesn’t have a charCodeAt() function.

Please let me know if you find it to be useful.

Projects using this

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27 Comments »

  1. 1. nicolas said on October 6th, 2008 at 9:53 pm #

    dud, how i use this script? what variable do i parse

    grettings from chile

  2. 2. Peter Chng said on October 28th, 2008 at 9:41 pm #

    The function is for taking an encoded polyline; it then returns an array of the points that make up the polyline.

    The polyline is an encoded string according to Google’s polyline algorithm.

    This is not a standalone script, it is merely a function that you can use in your own application.

  3. 3. Willem said on February 7th, 2009 at 5:49 am #

    I tested the script and the array looks fine! I’m going to use it, thanks!

  4. 4. Peter Chng said on February 7th, 2009 at 11:25 pm #

    @Willem
    Thanks for your support! If you create a project with it, let me know!

  5. 5. Hasnat said on January 15th, 2010 at 10:28 am #

    Thanks for this.
    P.S. Mark McClure is the actual code being used on google maps.

  6. 6. IPhone Application With MKMapView Using Unofficial Google Maps Directions API – kadir pekel said on May 29th, 2010 at 7:46 pm #

    […] contains a weird data that seems to be encoded. After some research i found Peter Chng’s blog post that points a php script that decodes encoded polyline data. I’d tried to port the script to […]

  7. 7. Luisja said on June 19th, 2010 at 7:46 am #

    many thanks Peter

  8. 8. Drawing Routes onto MKMapView Using Unofficial Google Maps Directions API « iPhone/iPad geeks world said on September 8th, 2010 at 7:25 am #

    […] which contains a weird data that seems to be encoded. After some research i found Peter Chng’s blog post that points a php script that decodes encoded polyline data. I’d tried to port the script to […]

  9. 9. Giuseppe Briotti said on September 18th, 2010 at 3:53 pm #

    It sounds great, I will test it but I must add the Zoom Levels string decoding too…

    Can I post the code when I’ll end it and if you like it.

  10. 10. Fiska said on November 25th, 2010 at 7:33 pm #

    Thanks guys, after i try your application, i want discuss with you..

  11. 11. Fiska said on November 25th, 2010 at 7:34 pm #

    i mean Google Maps Polyline Decoder in PHP

  12. 12. Ryan Sandigan said on February 3rd, 2011 at 6:04 am #

    Nice! You are a lifesaver. Thanks (:

  13. 13. Dino said on March 3rd, 2011 at 10:09 am #

    is there encoder?

  14. 14. Ryan Sandigan said on March 3rd, 2011 at 1:56 pm #

    I’m not sure but try this polyline encoder http://code.pulpmedia.at/php/polyline_encoder/

  15. 15. bboydev said on June 26th, 2011 at 4:19 am #

    thank you very much!

  16. 16. iPad???? MapKit???????? | ?????????? said on December 9th, 2011 at 12:42 am #

    […] which contains a weird data that seems to be encoded. After some research i found Peter Chng’s blog post that points a php script that decodes encoded polyline data. I’d tried to port the script to […]

  17. 17. Joe said on December 9th, 2011 at 11:20 pm #

    Great contribution man!

  18. 18. Gregor at GreenInfo Network said on June 6th, 2012 at 12:10 pm #

    Absolutely wonderful! You made short work of what would have taken me all day to figure out.

  19. 19. "on route" search for POI using Google Maps Web API, a PHP polyline decoder, PHP RouteBoxer, and MySQL | appsgoogleplus.com said on June 18th, 2012 at 9:52 pm #

    […] points in that file, decode these points with a php decoder ( php decoder obtained here: http://unitstep.net/blog/2008/08/02/decoding-google-maps-encoded-polylines-using-php/ ) included from another file, then create boxes to define the region near the route between the […]

  20. 20. Anshul Reejonia said on November 22nd, 2012 at 5:46 am #

    Thanks a lot for this.

  21. 21. Fredrik said on April 30th, 2013 at 9:14 am #

    Hi. Trying out your code. Having some trouble with it. Having some Google polyline saved in a mysql. Works great when working on a map.

    When serverside running your script the latitude is correct but the longitude shows wrong value.

    Any suggestions?

  22. 22. Fredrik said on April 30th, 2013 at 9:17 am #

    I tried the code in http://facstaff.unca.edu/mcmcclur/GoogleMaps/EncodePolyline/decode.html

    Gives same result as your PHP, but this is also wrong value for longitude. When loading the string on a google map I get correct lng value.

    Weird.

  23. 23. Chip Orange said on October 7th, 2014 at 9:41 am #

    FYI, Google static maps now support encoded polyline, in “path” parameter

  24. 24. Dave said on April 11th, 2015 at 2:33 pm #

    Works perfect for what I needed and will be implemented in the project at the URL above.

    Thank you so much for the work on this. I was digging through the encoding information starting to work it out backwards to decode it when I thought, “Someone has to have done this already!” And sure enough, you have! Thank you.

  25. 25. Hannes said on January 3rd, 2016 at 4:16 pm #

    Thanks a lot for this function! You want a beer? 🙂

  26. 26. Cedrick said on February 24th, 2016 at 8:06 pm #

    Thank you !

  27. 27. Alessandro Dias de Sá said on March 18th, 2016 at 2:41 pm #

    Thanks, you saved me.

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