Returns the coordinates constituting the boundary of a
set of cells which intersect or are contained by a polygon
(or polygons) specified in a shapefile. Note that grid cells
are also generated for holes in the shapefile's polygon(s).
Note that coordinates in the shapefile must be rounded to
check polygon intersections. Currently this round preserves
eight decimal digits of precision.
The eighth decimal place is worth up to 1.1 mm of precision:
this is good for charting the motions of tectonic plates and
the movements of volcanoes. Permanent, corrected,
constantly-running GPS base stations might be able to
achieve this level of accuracy.
In other words: you should be just fine with this level of
precision.