Merge remote-tracking branch 'upstream/pull/3016'

diff --combined lib/osm.rb
index 51e98f4aea86add9b98eb464afcc2e79646c9cf9,daa15fe8bffcaf8004411411dd7d6057a0478225..b6dd64b9986131b04fb6ddf6a1e9043f073a9240
--- 1/lib/osm.rb
--- 2/lib/osm.rb
+++ b/lib/osm.rb
@@@ -5,6 -5,13 +5,6 @@@ module OS
    require "rexml/text"
    require "xml/libxml"
  
 -  if defined?(SystemTimer)
 -    Timer = SystemTimer
 -  else
 -    require "timeout"
 -    Timer = Timeout
 -  end
 -
    # The base class for API Errors.
    class APIError < RuntimeError
      def initialize(message = "Generic API Error")
@@@ -371,12 -378,17 +371,17 @@@
      end
  
      # and these two will give you the right points on your image. all the constants can be reduced to speed things up. FIXME
+     # If the bbox has no extent, return the centre of the image to avoid dividing by zero.
  
      def y(lat)
+       return @height / 2 if (@by - @ty).zero?
+ 
        @height - ((ysheet(lat) - @ty) / (@by - @ty) * @height)
      end
  
      def x(lon)
+       return @width / 2 if (@bx - @tx).zero?
+ 
        ((xsheet(lon) - @tx) / (@bx - @tx) * @width)
      end
    end