code: function(bbox) {
          var xmin = Math.min(bbox[0][0], bbox[1][0]);
          var ymin = Math.min(bbox[0][1], bbox[1][1]);
          var xmax = Math.max(bbox[0][0], bbox[1][0]);
          var ymax = Math.max(bbox[0][1], bbox[1][1]);
          return [ [ xmin, ymin ], [ xmin, ymax ], [ xmax, ymax ],
                  [ xmax, ymin ], [ xmin, ymin ] ];
      }
docs: ------------------------------------------------------------------------ Polygons 
  Transforms a bounding box to a closed clipping polygon with clockwise
  order of coordinates.
  
  @param bbox
  [[xmin,ymin],[xmax,ymax]]
  @return a clipping rectangle with the following coordinates:
  [[xmin,ymin],[xmin,ymax],[xmax,ymax],[xmax,ymin],[xmin,ymin]]