Reference : http://www.maani.us/xml_charts/index.php?menu=Reference
chart_type = bar, circle, line, column (default), stacked column, floating column, 3d column, image column, stacked 3d column, parallel 3d column, pie, 3d pie, image pie, stacked bar, floating bar, area, stacked area, 3d area, stacked 3d area, candlestick, scatter, polar, bubble
chart1.xml chart_type = 3d pie
chart2.xml chart_type = bar
chart3.xml chart_type = stacked area
chart4.xml chart_type = parallel 3d column