This function draws a general user-defined curve defined by the
supplied Mapping. Note that the curve is transformed into graphical
coordinate space for plotting, so that a straight line in
physical coordinates may result in a curved line being drawn if
the Mapping involved is non-linear. Any discontinuities in the
Mapping between physical and graphical coordinates are
catered for, as is any clipping established using astClip.
If you need to draw simple straight lines (geodesics), astCurve
or astPolyCurve will usually be easier to use and faster.