public TileDirectory(){
  tilename="";
  this.tileID=-1;
  westlon=eastlon=northlat=southlat=Float.NaN;
}

public TileDirectory ( ) { tilename = "" ; this . tileID = - 1 ; westlon = eastlon = northlat = southlat = Float . NaN ; }
construct an untiled tiledirectory . since this object does not have valid boundaries , it is an error to call inregion on it
