Plot the edges (bare axis) of a soil texture triangle. This
is not a primary plot function, TT.baseplot() must have been
called before (usually inside TT.plot()).
TT.edges(geo, text.tol = NULL, text.sum = NULL, blr.clock = NULL,
col.axis = NULL, plot.axis = TRUE, frame.bg.col = NULL,
lwd.axis = NULL, tri.sum.tst = NULL, tri.pos.tst = NULL,
bg = NULL)