You can choose to only display a vertical slice of the overall Gantt chart by explicitly specifying a date range with the method GanttGraph::SetDateRange(). This will cap any bars to only be displayed in between the start and end date given as parameters. For example specifying
$graph-> SetDateRange( "2001-12-20", "2002-01-20");
will show the part of the Gantt chart between the 20 Dec 2001 and 20 of January 2002. Please note that the format depends on the locale setting.