AsLines will panic if g can not be coerced into a set of lines.

AsMultiPolygon will panic if g is not a geom.MultiPolygon or geom.Polygon if it is a geom.Polygon, it will return a multipolygon containing just that polygon.

AsPolygon will panic if g is not a geom.Polygon.

Decode will panic if err is not nil otherwise return the geometry.