geo_polygon.rb

class GeoPolygon
	attr_reader :verts, :bbox, :data

	# poly: entire Feature. Does not support rings, first vertex must be same as last
	def initialize(poly)
		@verts = []
		poly['geometry']['coordinates'].each do |ring|
			ring.each do |coords|
				@verts << [coords[0], coords[1]]
			end
		end
		@bbox = get_bounding_box
		@data = poly['properties']
	end

	# data: {key: value, ...}
	def add_data(data)
		data.each do |field, value|
			@data[field] = value
		end
	end

	def to_json
		{
			"type" => "Feature", 
			"properties" => @data, 
			"geometry" => { 
				"type" => "Polygon", 
				"coordinates" => [@verts]
			}
		}
	end

	def contains_point?(point)
		point = point['geometry']['coordinates']
		return false if not point_in_bounding_box?(point)
		intersections = 0
		(0...@verts.size - 1).each do |i|
			if crosses_ray?(point, @verts[i], @verts[i + 1])
				if point[0] < interpolate_x_coord(point, @verts[i], @verts[i + 1])
					intersections += 1
				end
			end
		end
		return intersections % 2 == 1
	end

	def crosses_ray?(point, ep1, ep2)
		if ep1[1] < ep2[1] # upward
			return (point[1] >= ep1[1] and point[1] < ep2[1])
		elsif ep1[1] > ep2[1] # downward
			return (point[1] >= ep2[1] and point[1] < ep1[1])
		end
		false
	end

	def interpolate_x_coord(point, ep1, ep2)
		return ep1[0] if ep1[0] == ep2[0]
		ep1, ep2 = ep2, ep1 if ep2[0] < ep1[0] # ep2 must be the rightmost point
		m = (ep2[1] - ep1[1]).to_f / (ep2[0] - ep1[0])
		b = ep2[1].to_f - (m * ep2[0])
	   (point[1] - b).to_f / m
	end

	def get_bounding_box
		minX = maxX = @verts[0][0]
		minY = maxY = @verts[0][1]
		@verts.each do |vert|
			minX = vert[0] if vert[0] < minX
			maxX = vert[0] if vert[0] > maxX
			minY = vert[1] if vert[1] < minY
			maxY = vert[1] if vert[1] > maxY
		end
		{bottomLeft: [minX, minY], topRight: [maxX, maxY]}
	end

	def point_in_bounding_box?(point)
		return true if (point[0] >= @bbox[:bottomLeft][0] and point[0] <= @bbox[:topRight][0]) and 
							(point[1] >= @bbox[:bottomLeft][1] and point[1] <= @bbox[:topRight][1])
		false
	end

  def area
    area = 0
    (0...@verts.size - 1).each do |i|
      area += (@verts[i+1][1] + @verts[i][1]) / 2.0 * (@verts[i+1][0] - @verts[i][0])
    end
    area.abs
  end
end