Pad bbox
ps_pad_bbox(x, pad)
A bbox object (or numeric vector of length 4 indicating xmin, ymin, xmax, ymax). Object should not be long/lat.
A numeric vector indicating amount in metres to pad bbox. If vector of length 1, amount is added to all sides; if vector of length 4 amount is added to left, top, right and bottom, respectively.
modified object.