This function can be used to place vector artwork anywhere on the plot, or to add a ‘PowerPoint’ style background to the entire chart area.

ch.Plot ¼12               
ch.Metafile'apltext' (6 4)
View ch.Close

This will add the ‘APL’ artwork with the lower left corner at x=6, y=4 reference the chart axes. If the metafile has been saved with a placeable header it will use this to make it at the correct size, however you can have it stretched to fit an arbitrary rectangle by passing the required width and height in addition:

ch.Metafile'apltext' (6 4 6 3)

Again, the width and height are expressed in the co-ordinate system of the chart.

If you call this function before you have plotted any charts, the entire chart area has notional axes of x=0–432, y=0–324. This is probably the most convenient point to add an element such as a shaded backdrop. However you will need to set the ‘nowipe’ style to prevent the first chart from clearing the plotting region:

ch.Metafile'shade' (0 0 432 324)
ch.Set 'nowipe,nohalo' ª ch.Plot ¼12 

Note that the normal ‘halo’ effect around markers is also cancelled for better visual effect.

If you use -ve positions they are interpreted as the distance from the opposite corner of the chart area, so to place your logo in the top left corner (at its true size):

ch.Metafile 'mylogo' 10 ¯10

Note that you may omit the extra level of nesting in the function argument if you prefer.

See also ...
ch.Bitmap – add images to charts