NAME

Geo::Google::PolylineEncoder - encode lat/lngs to Google Maps Polylines

SYNOPSIS

  use Geo::Google::PolylineEncoder;

  my $points = [
		{ 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:

http://code.google.com/apis/maps/documentation/polylinealgorithm.html

The module is a port of Mark McClure's PolylineEncoder.js with some minor tweaks. The original can be found here:

http://facstaff.unca.edu/mcmcclur/GoogleMaps/EncodePolyline/

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".

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.

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.

METHODS

encode( \@points );

Encode the points into a string for use with Google Maps GPolyline.fromEncoded using a variant of the Douglas-Peucker algorithm and the Polyline encoding algorithm defined by Google.

Expects a reference to a @points array ala:

[
 { lat => 38.5, lon => -120.2 },
 { lat => 40.7, lon => -120.95 },
 { lat => 43.252, lon => -126.453 },
];

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.

TODO

Benchmarking, & maybe bring distance calcs in-line as Joel Rosenberg did: http://facstaff.unca.edu/mcmcclur/GoogleMaps/EncodePolyline/gmap_polyline_encoder.rb.txt

AUTHOR

Steve Purkis <spurkis@cpan.org>

Ported from Mark McClure's PolylineEncoder.js which can be found here: http://facstaff.unca.edu/mcmcclur/GoogleMaps/EncodePolyline/PolylineEncoder.html

Some encoding ideas borrowed from Geo::Google.

COPYRIGHT

Copyright (c) 2008 Steve Purkis. Released under the same terms as Perl itself.

SEE ALSO

http://code.google.com/apis/maps/documentation/polylinealgorithm.html, http://facstaff.unca.edu/mcmcclur/GoogleMaps/EncodePolyline/PolylineEncoder.html (JavaScript implementation), http://www.usnaviguide.com/google-encode.htm (similar implementation in perl), Geo::Google, JSON