NAME Geo::Google::PolylineEncoder - encode lat/lons to Google Maps Polylines SYNOPSIS use Geo::Google::PolylineEncoder; my $points = [ # can also take points as [lat, lon] { lat => 38.5, lon => -120.2 }, { lat => 40.7, lon => -120.95 }, { lat => 43.252, lon => -126.453 }, ]; my $encoder = Geo::Google::PolylineEncoder->new; my $eline = $encoder->encode( $points ); print $eline->{num_levels}; # 18 print $eline->{zoom_factor}; # 2 print $eline->{points}; # _p~iF~ps|U_ulLnnqC_mqNvxq`@ print $eline->{levels}; # POP # in Javascript, assuming eline was encoded as JSON: # ... load GMap2 ... var opts = { points: eline.points, levels: eline.levels, numLevels: eline.num_levels, zoomFactor: eline.zoom_factor, }; var line = GPolyline.fromEncoded( opts ); DESCRIPTION This module encodes a list of lat/lon points representing a polyline into a format for use with Google Maps. This format is described here: The module is a port of Mark McClure's "PolylineEncoder.js" with some tweaks. The original can be found here: CONSTRUCTOR & ACCESSORS new( [%args] ) Create a new encoder. Arguments are optional and correspond to the accessor with the same name: "num_levels", "zoom_factor", "visible_threshold", "force_endpoints", etc... Note: there's nothing stopping you from setting these properties each time you "encode" a polyline. num_levels How many different levels of magnification the polyline has. Default: 18. zoom_factor The change in magnification between those levels (see "num_levels"). Default: 2. visible_threshold Indicates the length of a barely visible object at the highest zoom level. Default: 0.00001. err.. units. force_endpoints Indicates whether or not the endpoints should be visible at all zoom levels. force_endpoints is. Probably should stay true regardless. Default: 1=true. escape_encoded_points Indicates whether or not the encoded points should have escape characters escaped, eg: $points =~ s/\\/\\\\/g; This is useful if you'll be evalling the resulting strings, or copying them into a static document. Warning: don't turn this on if you'll be passing the encoded points straight on to your application, or you'll get unexpected results (ie: lines that start out right, but end up horribly wrong). It may even crash your browser. Default: 0=false. lons_first Specifies the order in which coordinates passed as arrayrefs to "encode" should be interpreted: # false: lat, lon $encoder->encode([ [ 38.5, -120.2 ], [ 40.7, -120.95 ], ]); # true: lon, lat $encoder->encode([ [ -120.2, 38.5 ], [ -120.95, 40.7 ], ]); Default: 0 = lat,lon (Yes, the default feels wrong to the mathematician in me, but that's how Google Maps do it, so for sake of consistency...) METHODS encode( \@points ); Encode the points into a string for use with Google Maps "GPolyline.fromEncoded" using a variant of the Douglas-Peucker algorithm to set levels, and the Polyline encoding algorithm defined by Google. Expects a reference to a @points array: [ { lat => 38.5, lon => -120.2 }, { lat => 40.7, lon => -120.95 }, { lat => 43.252, lon => -126.453 }, ]; The individual points can also be given as arrayrefs: [ [ 38.5, -120.2 ], [ 40.7, -120.95 ], [ 43.252, -126.453 ], ]; *Note:* I tried to avoid this initially, because there's no standard for which should come first: *lat*s or *lon*s. But I agree, it's more convenient in some cases so I've given you enough rope to hang yourself... Of course you can easily unhang yourself: the order for arrayrefs defaults to "lat, lon", but you can change that by setting "lons_first". Returns a hashref containing: { points => 'encoded points string', levels => 'encoded levels string', num_levels => int($num_levels), zoom_factor => int($zoom_factor), }; You can then use the JSON modules (or XML, or whatever) to pass the encoded values to your Javascript application for use there. decode_points( $encoded_polyline ); Given an encoded polyline, returns the points: [ { lat => 38.5, lon => -120.2 }, { lat => 40.7, lon => -120.95 }, { lat => 43.252, lon => -126.453 }, ]; Note that these will likely be slightly different from the original points due to rounding errors during both "encode" & decoding. decode_levels( $encoded_levels ); Given encoded levels, returns the levels: [ 17, 16, 17 ] WHY DO MY LINES LOOK FUNNY? Do your lines all go through the north pole? Maybe you have your *lon*s & *lat*s mixed up... If so and you're using point arrays, you can set "lons_first". Do your points not show up at particular zoom levels? That's not a bug, it's a feature! Try playing with "visible_threshold". Do your encoded lines cause your browser to crash? Sounds like a bug - file it! BUGS TODO More optimization: encoding big files is *slow*. Maybe XS implementation if there's enough demand for it? AUTHOR Steve Purkis Ported from Mark McClure's "PolylineEncoder.js" which can be found here: Some encoding ideas borrowed from Geo::Google. Bringing distance calcs in-line was Joel Rosenberg's idea: COPYRIGHT Copyright (c) 2008-2010 Steve Purkis. Released under the same terms as Perl itself. SEE ALSO , (JavaScript implementation), (similar implementation in perl), Geo::Google, JSON::Any