Helper map user's coordinates to pixels
coord_to_px(coord, coordmap, clipedge = FALSE)
a 2-columns matrix with "x" and "y" coordinates.
coordinates in user system. A matrix where rows are points and with at least 2 columns named "x" and "y" for x and y coordinates, respectively.
current device adjusted coordinates. Default is missing.
whether to clip points outside of plotting region to the edge. Default is FALSE.