Added encoded polyline support by including Joel Rosenberg's GMapPoly…

…lineEncoder class. Also added helper methods to create encoded polylines and encoded polylines from GeoRuby objects.

(cherry picked from commit f94c3d1)

lib/gm_plugin/encoder.rb

@@ -0,0 +1,395 @@
+#--
+#
+# Utility for creating Google Maps Encoded GPolylines
+#
+# License: You may distribute this code under the same terms as Ruby itself
+#
+# Author: Joel Rosenberg
+# Modified for use in YM4R by Ken-ichi Ueda
+#
+# ( Drawing from the official example pages as well as Mark McClure's work )
+#
+# == Example
+#
+#   data = [
+#     [ 37.4419, -122.1419],
+#     [ 37.4519, -122.1519],
+#     [ 37.4619, -122.1819],
+#   ]
+#
+#   encoder = GMapPolylineEncoder.new()
+#   result = encoder.encode( data )
+#
+#   javascript << "  var myLine = new GPolyline.fromEncoded({\n"
+#   javascript << "     color: \"#FF0000\",\n"
+#   javascript << "     weight: 10,\n"
+#   javascript << "     opacity: 0.5,\n"
+#   javascript << "     zoomFactor: #{result[:zoomFactor]},\n"
+#   javascript << "     numLevels: #{result[:numLevels]},\n"
+#   javascript << "     points: \"#{result[:points]}\",\n"
+#   javascript << "     levels: \"#{result[:levels]}\"\n"
+#   javascript << "  });"
+#
+# == Methods
+#
+#   Constructor args (all optional): 
+#     :numLevels (default 18)
+#     :zoomFactor (default 2)
+#     :reduce: Reduce points (default true)
+#     :escape: Escape backslashes (default true)
+#
+#   encode( points ) method
+#     points (required): array of longitude, latitude pairs
+#
+#     returns hash with keys :points, :levels, :zoomFactor, :numLevels
+#
+# == Background
+#
+# Description: http://www.google.com/apis/maps/documentation/#Encoded_Polylines
+# API: http://www.google.com/apis/maps/documentation/reference.html#GPolyline
+# Hints: http://www.google.com/apis/maps/documentation/polylinealgorithm.html
+#
+# Example Javascript for instantiating an encoded polyline:
+# var encodedPolyline = new GPolyline.fromEncoded({
+#     color: "#FF0000",
+#     weight: 10,
+#     points: "yzocFzynhVq}@n}@o}@nzD",
+#     levels: "BBB",
+#     zoomFactor: 32,
+#     numLevels: 4
+# });
+#
+# == Changes
+#
+# 06.29.2007 - Release 0.1
+#            Profiling showed that distance() accounted for 50% of the time when
+#            processing McClure's British coast data. By moving the distance
+#            calculation into encode(), we can cache a few of the calculations
+#            (magnitude) and eliminate the overhead of the function call. This
+#            reduced the time to encode by ~ 30%
+#
+# 06.21.2007 Implementing the Doublas-Peucker algorithm for removing superflous
+#            points as per Mark McClure's design:
+#                http://facstaff.unca.edu/mcmcclur/GoogleMaps/EncodePolyline/
+#
+# 10.14.2006 Cleaned up (and finally grasped) zoom levels
+#
+# 09.2006    First port of the official example's javascript. Ignoring zoom
+#            levels for now, showing points at all zoom levels
+#
+#++
+
+module Ym4r
+  module GmPlugin
+    class GMapPolylineEncoder
+      attr_accessor :reduce, :escape #zoomFactor and numLevels need side effects
+      attr_reader :zoomFactor, :numLevels
+
+      # The minimum distance from the line that a point must exceed to avoid
+      # elimination under the DP Algorithm.
+      @@dp_threshold = 0.00001
+
+      def initialize(options = {})
+        # There are no required parameters
+
+        # Nice defaults
+        @numLevels  = options.has_key?(:numLevels)  ? options[:numLevels]  : 18
+        @zoomFactor = options.has_key?(:zoomFactor) ? options[:zoomFactor] : 2
+
+        # Calculate the distance thresholds for each zoom level
+        calculate_zoom_breaks()
+
+        # By default we'll simplify the polyline unless told otherwise
+        @reduce = ! options.has_key?(:reduce) ? true : options[:reduce]
+
+        # Escape by default; most people are using this in a web context
+        @escape = ! options.has_key?(:escape) ? true : options[:escape]
+
+      end
+
+      def numLevels=( new_num_levels )
+        @numLevels = new_num_levels
+        # We need to recalculate our zoom breaks
+        calculate_zoom_breaks()
+      end
+
+      def zoomFactor=( new_zoom_factor )
+        @zoomFactor = new_zoom_factor
+        # We need to recalculate our zoom breaks
+        calculate_zoom_breaks()
+      end
+
+      def encode( points )
+
+        #
+        # This is an implementation of the Douglas-Peucker algorithm for simplifying
+        # a line. You can thing of it as an elimination of points that do not
+        # deviate enough from a vector. That threshold for point elimination is in
+        # @@dp_threshold. See
+        #
+        #   http://everything2.com/index.pl?node_id=859282
+        #
+        # for an explanation of the algorithm
+        #
+
+        max_dist = 0  # Greatest distance we measured during the run
+        stack = []
+        distances = Array.new(points.size)
+
+        if(points.length > 2)
+          stack << [0, points.size-1]
+
+          while(stack.length > 0) 
+            current_line = stack.pop()
+            p1_idx = current_line[0]
+            pn_idx = current_line[1]
+            pb_dist = 0
+            pb_idx = nil
+
+            x1 = points[p1_idx][0]
+            y1 = points[p1_idx][1]
+            x2 = points[pn_idx][0]
+            y2 = points[pn_idx][1]
+
+            # Caching the line's magnitude for performance
+            magnitude = Math.sqrt((x2 - x1)**2 + (y2 - y1)**2)
+            magnitude_squared = magnitude ** 2
+
+            # Find the farthest point and its distance from the line between our pair
+            for i in (p1_idx+1)..(pn_idx-1)
+
+              # Refactoring distance computation inline for performance
+              #current_distance = compute_distance(points[i], points[p1_idx], points[pn_idx])
+
+              # 
+              # This uses Euclidian geometry. It shouldn't be that big of a deal since
+              # we're using it as a rough comparison for line elimination and zoom
+              # calculation.
+              #
+              # TODO: Implement Haversine functions which would probably bring this to
+              #       a snail's pace (ehhhh)
+              #
+
+              px = points[i][0]
+              py = points[i][1]
+
+              current_distance = nil
+
+              if( magnitude == 0 )
+                # The line is really just a point
+                current_distance = Math.sqrt((x2-px)**2 + (y2-py)**2)
+              else
+
+                u = (((px - x1) * (x2 - x1)) + ((py - y1) * (y2 - y1))) / magnitude_squared
+
+                if( u <= 0 || u > 1 )
+                    # The point is closest to an endpoint. Find out which one
+                    ix = Math.sqrt((x1 - px)**2 + (y1 - py)**2)
+                    iy = Math.sqrt((x2 - px)**2 + (y2 - py)**2)
+                    if( ix > iy )
+                      current_distance = iy
+                    else
+                      current_distance = ix
+                    end
+                else
+                    # The perpendicular point intersects the line
+                    ix = x1 + u * (x2 - x1)
+                    iy = y1 + u * (y2 - y1)
+                    current_distance = Math.sqrt((ix - px)**2 + (iy - py)**2)
+                end
+              end
+
+              # See if this distance is the greatest for this segment so far
+              if(current_distance > pb_dist)
+                pb_dist = current_distance
+                pb_idx = i
+              end
+            end
+
+            # See if this is the greatest distance for all points
+            if(pb_dist > max_dist)
+              max_dist = pb_dist
+            end
+
+            if(pb_dist > @@dp_threshold)
+              # Our point, Pb, that had the greatest distance from the line, is also
+              # greater than our threshold. Process again using Pb as a new 
+              # start/end point. Record this distance - we'll use it later when
+              # creating zoom values
+              distances[pb_idx] = pb_dist
+              stack << [p1_idx, pb_idx]
+              stack << [pb_idx, pn_idx]
+            end
+
+          end
+        end
+
+        # Force line endpoints to be included (sloppy, but faster than checking for
+        # endpoints in encode_points())
+        distances[0] = max_dist
+        distances[distances.length-1] = max_dist
+
+        # Create Base64 encoded strings for our points and zoom levels
+        points_enc = encode_points( points, distances)
+        levels_enc = encode_levels( points, distances, max_dist)
+
+        # Make points_enc an escaped string if desired.
+        # We should escape the levels too, in case google pulls a switcheroo
+        @escape && points_enc && points_enc.gsub!( /\\/, '\\\\\\\\' )
+
+
+        # Returning a hash. Yes, I am a Perl programmer
+        return {
+          :points     => points_enc,
+          :levels     => levels_enc,
+          :zoomFactor => @zoomFactor,
+          :numLevels  => @numLevels,
+        }
+
+      end
+
+      private
+
+      def calculate_zoom_breaks()
+        # Calculate the distance thresholds for each zoom level
+        @zoom_level_breaks = Array.new(@numLevels);
+
+        for i in 0..(@numLevels-1)
+          @zoom_level_breaks[i] = @@dp_threshold * (@zoomFactor ** ( @numLevels-i-1));
+        end
+
+        return
+      end
+
+      def encode_points( points, distances )
+        encoded = ""
+
+        plat = 0
+        plon = 0
+
+        #points.each do |point| # Gah, need the distances.
+        for i in 0..(points.size() - 1)
+          if(! @reduce || distances[i] != nil )
+            point = points[i]
+            late5 = (point[0] * 1e5).floor();
+            lone5 = (point[1] * 1e5).floor();
+
+            dlat = late5 - plat
+            dlon = lone5 - plon
+
+            plat = late5;
+            plon = lone5;
+
+            # I used to need this for some reason
+            #encoded << encodeSignedNumber(Fixnum.induced_from(dlat)).to_s
+            #encoded << encodeSignedNumber(Fixnum.induced_from(dlon)).to_s
+            encoded << encodeSignedNumber(dlat).to_s
+            encoded << encodeSignedNumber(dlon).to_s
+          end
+        end
+
+        return encoded
+
+      end
+
+      def encode_levels( points, distances, max_dist )
+
+        encoded = "";
+
+        # Force startpoint
+        encoded << encodeNumber(@numLevels - 1)
+
+        if( points.size() > 2 )
+          for i in 1..(points.size() - 2)
+            distance = distances[i]
+            if( ! @reduce || distance != nil)
+              computed_level = 0
+
+              while (distance < @zoom_level_breaks[computed_level]) do
+                computed_level += 1
+              end
+
+              encoded << encodeNumber( @numLevels - computed_level - 1 )
+            end
+          end
+        end
+
+        # Force endpoint
+        encoded << encodeNumber(@numLevels - 1)
+
+        return encoded;
+
+      end
+
+      def compute_distance( point, lineStart, lineEnd )
+
+        #
+        # Note: This has been refactored to encode() inline for performance and 
+        #       computation caching
+        #
+
+        px = point[0]
+        py = point[1]
+        x1 = lineStart[0]
+        y1 = lineStart[1]
+        x2 = lineEnd[0]
+        y2 = lineEnd[1]
+
+        distance = nil
+
+        magnitude = Math.sqrt((x2 - x1)**2 + (y2 - y1)**2)
+
+        if( magnitude == 0 )
+          return Math.sqrt((x2-px)**2 + (y2-py)**2)
+        end
+
+        u = (((px - x1) * (x2 - x1)) + ((py - y1) * (y2 - y1))) / (magnitude**2)
+
+        if( u <= 0 || u > 1 )
+            # The point is closest to an endpoint. Find out which
+            ix = Math.sqrt((x1 - px)**2 + (y1 - py)**2)
+            iy = Math.sqrt((x2 - px)**2 + (y2 - py)**2)
+            if( ix > iy )
+              distance = iy
+            else
+              distance = ix
+            end
+        else
+            # The perpendicular point intersects the line
+            ix = x1 + u * (x2 - x1)
+            iy = y1 + u * (y2 - y1)
+            distance = Math.sqrt((ix - px)**2 + (iy - py)**2)
+        end
+
+        return distance
+      end
+
+      def encodeSignedNumber(num)
+        # Based on the official google example
+
+        sgn_num = num << 1
+
+        if( num < 0 )
+            sgn_num = ~(sgn_num)
+        end
+
+        return encodeNumber(sgn_num)
+      end
+
+      def encodeNumber(num)
+        # Based on the official google example
+
+        encoded = "";
+
+        while (num >= 0x20) do
+            encoded << ((0x20 | (num & 0x1f)) + 63).chr;
+            num = num >> 5;
+        end
+
+        encoded << (num + 63).chr;
+        return encoded;
+      end
+
+    end
+  end
+end