path_detalizing.rb

module Spatial::Utils
  EARTH_RADIUS = 6371.0
  DETAILED_THRESHOLD = 3.0 # meters

  module_function
  def distance(point1, point2)
    point1 = to_radians(point1)
    point2 = to_radians(point2)

    dlat = point2[0] - point1[0]
    dlon = point2[1] - point1[1]

    a = (Math.sin(dlat / 2))**2 + Math.cos(point1[0]) *
        (Math.sin(dlon / 2))**2 * Math.cos(point2[0])
    c = 2 * Math.atan2( Math.sqrt(a), Math.sqrt(1-a))
    c * EARTH_RADIUS * 1000
  end

  def distance_path(path)
    dist = 0
    prev_point = path[0]
    path[1..-1].each do |point|
      dist += distance prev_point, point
      prev_point = point
    end
    dist
  end

  def to_radians(point)
    point.map{|coord|coord * (Math::PI / 180)}
  end

  def interpolate_point(point1, point2, fraction)
    x1 = point1[0]
    y1 = point1[1]
    x2 = point2[0]
    y2 = point2[1]

    [
      (x1 + (x2 - x1) * fraction),
      (y1 + (y2 - y1) * fraction)
    ]
  end

  def make_detalized(path)
    detailed_path = [path[0]]
    prev_point = path[0]

    path[1..-1].each do |point|
      cur_distance = distance prev_point, point
      if cur_distance > DETAILED_THRESHOLD
        min_fraction = DETAILED_THRESHOLD / cur_distance
        puts min_fraction
        i = 1
        while (fraction = i * min_fraction) <= 1
          detailed_path.push interpolate_point(point, prev_point, fraction)
          i += 1
        end
      end
      detailed_path.push point
      prev_point = point
    end

    return detailed_path
  end

  def make_detalized_from_wkt(wkt)
    make_detalized parse_wkt wkt
  end

  def parse_wkt(wkt_line_string)
    points = wkt_line_string[/LINESTRING.*\((.*)\)/,1]
    points.split(',').map{ |point| point.split(' ').reverse.map(&:to_f) }
  end

  def path_to_wkt(path)
    path = path.map{ |point| point.reverse.join(' ') }.join(',')
    "LINESTRING(#{path})"
  end

end