Only "x", "y" "n" and "pos" are required in col.
If "id" is not specified, a numerical identifier will be automatically created.
proj defines projection used by data. It could be a character string
corresponding to a PROJ.4 projection (see https://proj.org/
for more details) or an object of class sp::CRS.
If the projection of boundary is defined in a slot called proj4string,
boundary will be projected according to proj. If the slot proj4string
is missing, boundary will be considered to be already in the same projection as proj.
If boundary is not defined (NULL), a considered corresponding to minimal
and maximal coordinates of data will be used.
boundary could be the result of the function create.boundary().
It's not possible to change projection of data with as.prevR().
Use changeproj() instead.