code: def fence_draw_callback(self, points):
          '''callback from drawing a fence'''
          self.fenceloader.clear()
          if len(points) < 3:
              return
          self.fenceloader.target_system = self.target_system
          self.fenceloader.target_component = self.target_component
          bounds = mp_util.polygon_bounds(points)
          (lat, lon, width, height) = bounds
          center = (lat+width/2, lon+height/2)
          self.fenceloader.add_latlon(center[0], center[1])
          for p in points:
              self.fenceloader.add_latlon(p[0], p[1])
          # close it
          self.fenceloader.add_latlon(points[0][0], points[0][1])
          self.send_fence()
          self.have_list = Truf fence_draw_callback(self, points):
          '''callback from drawing a fence'''
          self.fenceloader.clear()
          if len(points) < 3:
              return
          self.fenceloader.target_system = self.target_system
          self.fenceloader.target_component = self.target_component
          bounds = mp_util.polygon_bounds(points)
          (lat, lon, width, height) = bounds
          center = (lat+width/2, lon+height/2)
          self.fenceloader.add_latlon(center[0], center[1])
          for p in points:
              self.fenceloader.add_latlon(p[0], p[1])
          # close it
          self.fenceloader.add_latlon(points[0][0], points[0][1])
          self.send_fence()
          self.have_list = True
docs: callback from drawing a fence