def distance(other)
			unless other.is_a? Point
				raise ArgumentError.new 'other must be a Point.'
			end

			dlng = GpsUtils::to_radians(other.lng - @lng)
			dlat = GpsUtils::to_radians(other.lat - @lat)

			x = dlng * Math.cos(dlat / 2)
			y = GpsUtils::to_radians(other.lat - @lat)

			Math.sqrt(x**2 + y**2) * GpsUtils::R
		end
def distance(other)
			unless other.is_a? Point
				raise ArgumentError.new 'other must be a Point.'
			end

			dlng = GpsUtils::to_radians(other.lng - @lng)
			dlat = GpsUtils::to_radians(other.lat - @lat)

			x = dlng * Math.cos(dlat / 2)
			y = GpsUtils::to_radians(other.lat - @lat)

			Math.sqrt(x**2 + y**2) * GpsUtils::R
		end
Measure the distance between this point and another.

 Distance is calculated using equirectangular projection.
 @see https://en.wikipedia.org/wiki/Equirectangular_projection

 @param other [Point]
 @return [Float]
 @raise [ArgumentError] if other is not a Point