Method: MapKit::ZoomLevel::ClassMethods#coordinate_region_with_map_view

Defined in:
lib/map-kit-wrapper/zoom_level.rb

#coordinate_region_with_map_view(map_view, center_coordinate, zoom_level) ⇒ Object

Get the coordiante region for the given zoom level

This would involve wrapping the map from top to bottom, something that a Mercator projection just cannot do.

  • Args :

    • map_view -> A MKMapView

    • center_coordinates -> Coordinates as MKMapPoint

    • zoom_level -> Zoom level as Int

  • Returns :

    • Region as MKCoordinateRegion



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# File 'lib/map-kit-wrapper/zoom_level.rb', line 141

def coordinate_region_with_map_view(map_view, center_coordinate, zoom_level)

  # clamp lat/long values to appropriate ranges
  center_coordinate.latitude = [[-90.0, center_coordinate.latitude].max, 90.0].min
  center_coordinate.longitude = center_coordinate.longitude % 180.0

  # convert center coordiate to pixel space
  center_pixel_x = self.longitude_to_pixel_space_x(center_coordinate.longitude)
  center_pixel_y = self.latitude_to_pixel_space_y(center_coordinate.latitude)

  # determine the scale value from the zoom level
  zoom_exponent = 20 - zoom_level
  zoom_scale = 2 ** zoom_exponent

  # scale the map’s size in pixel space
  map_size_in_pixels = map_view.bounds.size
  scaled_map_width = map_size_in_pixels.width * zoom_scale
  scaled_map_height = map_size_in_pixels.height * zoom_scale

  # figure out the position of the left pixel
  top_left_pixel_x = center_pixel_x - (scaled_map_width / 2)

  # find delta between left and right longitudes
  min_lng = self.pixel_space_x_to_longitude(top_left_pixel_x)
  max_lng = self.pixel_space_x_to_longitude(top_left_pixel_x + scaled_map_width)
  longitude_delta = max_lng - min_lng

  # if we’re at a pole then calculate the distance from the pole towards the equator
  # as MKMapView doesn’t like drawing boxes over the poles
  top_pixel_y = center_pixel_y - (scaled_map_height / 2)
  bottom_pixel_y = center_pixel_y + (scaled_map_height / 2)
  adjusted_center_point = false
  if top_pixel_y > MERCATOR_OFFSET * 2
    top_pixel_y = center_pixel_y - scaled_map_height
    bottom_pixel_y = MERCATOR_OFFSET * 2
    adjusted_center_point = true
  end

  # find delta between top and bottom latitudes
  min_lat = self.pixel_space_y_to_latitude(top_pixel_y)
  max_lat = self.pixel_space_y_to_latitude(bottom_pixel_y)
  latitude_delta = -1 * (max_lat - min_lat)

  # create and return the lat/lng span
  span = MKCoordinateSpanMake(latitude_delta, longitude_delta)
  region = MKCoordinateRegionMake(center_coordinate, span)
  # once again, MKMapView doesn’t like drawing boxes over the poles
  # so adjust the center coordinate to the center of the resulting region
  if adjusted_center_point
    region.center.latitude = self.pixel_space_y_to_latitude((bottom_pixel_y + top_pixel_y) / 2.0)
  end

  region
end