Add geometry calculation support for ActiveRecord using PostGIS.

geometry_support.rb

# Add geometry calculation support.
# extend this module for ActiveRecord model.
module GeometrySupport

  def by_distance_from_center(center, opts = {})
    opts.reverse_merge! :meters => 500
    cp = LatLng.from(center).to_point
    sw_ne = boundary_from_meters(center,
                                 opts[:meters]).map {|ll| ll.to_point}
    cc = ComplexCondition.new
    cc.push "SetSRID(MakeBox3D(GeomFromText(?, #{LatLng::WGS84}), GeomFromText(?, #{LatLng::WGS84})), #{LatLng::WGS84}) && location", sw_ne[0].as_text, sw_ne[1].as_text
    cc.push "distance_sphere(location, GeomFromText(?, #{LatLng::WGS84})) < #{opts[:meters]}", cp.as_text
    self.where(cc.conditions).
        select("*, distance_sphere(location, GeomFromText('#{cp.as_text}', #{LatLng::WGS84})) as distance").
        order('distance')
  end

  def count_from_center(center, opts = {})
    opts.reverse_merge! :meters => 500
    cp = LatLng.from(center).to_point
    sw_ne = boundary_from_meters(center,
                                 opts[:meters]).map {|ll| ll.to_point}
    cc = ComplexCondition.new
    cc.push "SetSRID(MakeBox3D(GeomFromText(?, #{LatLng::WGS84}), GeomFromText(?, #{LatLng::WGS84})), #{LatLng::WGS84}) && location", sw_ne[0].as_text, sw_ne[1].as_text
    cc.push "distance_sphere(location, GeomFromText(?, #{LatLng::WGS84})) < #{opts[:meters]}", cp.as_text
    self.where(cc.conditions).count
  end

  private
  EN = 20 * 60 * 60
  def meter_to_unit(meters)
    meters.to_f / EN.to_f
  end

  def boundary_from_meters(center, meters)
    m = meters.to_f
    c = LatLng.from(center)
    unit = meter_to_unit(m)
    cu = LatLng.new(c.lat + unit, c.lng).to_point
    cr = LatLng.new(c.lat, c.lng + unit).to_point
    cp = c.to_point
    distance_lat = cu.distance(cp)
    distance_lng = cr.distance(cp)
    ll_ofs = LatLng.new(unit / distance_lat * m,
                          unit / distance_lng * m)
    cll = c - ll_ofs
    cur = c + ll_ofs
    [cll, cur]
  end

end