code: function(newParams, altUrl) {
          // use layer's url unless altUrl passed in
          var url = (altUrl == null) ? this.url : altUrl;
          
          // if url is not a string, it should be an array of strings, 
          //  in which case we will randomly select one of them in order
          //  to evenly distribute requests to different urls.
          if (typeof url == "object") {
              url = url[Math.floor(Math.random()*url.length)];
          }   
          // requestString always starts with url
          var requestString = url;        
  
          var tileRowGroup = "";
          var tileColGroup = "";
          
          if (newParams.tilerow < 0) {
            tileRowGroup =  '-';
          }
            
          if (newParams.tilerow == 0 ) {
            tileRowGroup += '0';
          } else {
            tileRowGroup += Math.floor(Math.abs(newParams.tilerow/this.params.tileRowsPerFolder)) * this.params.tileRowsPerFolder;
          }
            
          if (newParams.tilecol < 0) {
            tileColGroup =  '-';
          }
          
          if (newParams.tilecol == 0) {
            tileColGroup += '0';
          } else {
            tileColGroup += Math.floor(Math.abs(newParams.tilecol/this.params.tileColumnsPerFolder)) * this.params.tileColumnsPerFolder;
          }
          
          var tilePath = '/S' + Math.floor(newParams.scaleindex)
                  + '/' + this.params.basemaplayergroupname
                  + '/R' + tileRowGroup
                  + '/C' + tileColGroup
                  + '/' + (newParams.tilerow % this.params.tileRowsPerFolder) 
                  + '_' + (newParams.tilecol % this.params.tileColumnsPerFolder) 
                  + '.' + this.params.format;
      
          if (this.params.querystring) {
                 tilePath += "?" + this.params.querystring;
          }
          
          requestString += tilePath;
          return requestString;
      }
docs: Method: getImageFilePath
  special handler to request mapguide tiles from an http exposed tilecache
  
  Parameters:
  altUrl - {String} Alternative base URL to use.
  
  Returns:
  {String} A string with the url for the tile image