rspecdata
(required) a data frame, possibly an object of class rspec
that has wavelength range in the first column, named 'wl', and spectral measurements in the
remaining columns.
legpos
legend position control. Either a vector containing x and y coordinates
or a single keyword from the list: "bottomright", "bottom", "bottomleft",
"left", "topleft", "top", "topright", "right" and "center".