if TRUE then this plot will be added to any existing plot.
Note that if back.col (see below) is specified then a new plot
window will be opened and add = TRUE will have no effect
type
a single character indicating the type of item to plot.
Supported types are: 'p' for points, 's' for spheres, 'l' for lines,
'h' for line segments from z = 0, and 'n' for nothing.
col
specify the colour(s) of the plotted points
size
the size of plotted points
box
whether to draw a box
axes
whether to draw axes
aspect
either a logical indicating whether to adjust the
aspect ratio, or a new ratio.
back.col
specifies the background colour of
the plot. This argument is passed to rgl::bg3d.
depth_test
The depth test to be applied.
This controls how resistant the plotted
object is to being obscured.
See rgl.material