Combine several polygons into a single polygon by modifying the
PID and SID indices.
combinePolys (polys)PolySet with one or more polygons, each with possibly several components/holes.
PolySet, possibly with the addition of an SID column if
it did not already exist. The function may also reorder columns such
that PID, SID, POS, X and Y appear
first, in that order.
This function accepts a PolySet containing one or more polygons
(PIDs), each with one or more components or holes
(SIDs). The SID column need not exist in the input.
The function combines these polygons into a single polygon by simply
renumbering the PID and SID indices. The resulting
PolySet contains a single PID (with the value 1) and uses
the SID value to differentiate between polygons, their
components, and holes.