public boolean visitNode(IGridNode n)
{
IGridHost host = n.getMachine();
if ( isValid && host instanceof TileController )
{
TileController c = (TileController) host;
minX = Math.min( c.xCoord, minX );
maxX = Math.max( c.xCoord, maxX );
minY = Math.min( c.yCoord, minY );
maxY = Math.max( c.yCoord, maxY );