Graphics examples showing how to draw the detector output on the map and
on the spectrogram display.
The class GeneralProjector knows how to turn parameters such as lat, long, time,
frequency into meaningful screen coordinates. It will tell us which types
of coordinates are required for each display, if we can provide them we can
go ahead and draw. The canDraw function is mainly used by Pamguard for making
up options menus of what can be plotted on top of the various displays. The
PanelOverlayDraw is attached to a specific data block, so this one class needs
to handle drawing on all different types of display.