[GRASS-dev] g.region: a possible extension to support multiple zoom= and mode=intersect

[Ivan Shmakov]

	As `zoom=' somewhat mimics `rast=', wouldn't it be natural to
	extend `zoom=' to allow multiple rasters?

	Allowing multiple rasters for `zoom=' may make one wonder about
	some further extensions.  Firstly, wouldn't it be useful to
	allow both `rast=' and `zoom=' be specified at the same time to
	calculate the least region covering both the `rast=' and `zoom='
	rasters (with the usual `rast=' and `zoom=' behaviour still
	followed)?  What about adding `vect=' and `region=' as well?

	Secondly, the above extensions make it easy to compute set union
	(or rather its boundary box) of the regions (specified as named
	regions, rasters or vectors), but it seems to be useful to allow
	one to calculate set intersection as well.  Hence,
	`mode=intersect' as a counterpart to the default `mode=union'
	(or `mode=traditional'?)

	Please note that the last change is somewhat disturbing to the
	existing code, since the result of the intersection may well be
	an empty region, while AFAIK there's no conception of empty
	region in GRASS currently.