[GRASS5] D.zoom behavior

Glynn Clements glynn.clements at virgin.net
Sun Sep 12 18:31:23 EDT 2004

Michael Barton wrote:

> I  agree with you overall. But in regards to #2 below, I would go even
> further. D.zoom is described as an interactive way to change the region
> extents. IMHO, this is what it should be. It should not be necessary to have
> anything displayed in order to change the region extents in this way (It is
> not necessary to have anything displayed in order to run g.region). IOW, you
> should be able to open a monitor, display nothing, create a zoom box using
> d.zoom, and change the region extents accordingly. Any *subsequently*
> displayed map would use those extents. If anything *is* displayed, the
> region change would be followed by a screen redraw of course.

That would certainly work, although I suspect that it's likely to be
pointless. I can't imagine anyone wanting to set the region by marking
a rectangle on a blank window. When you use d.zoom, you invariably
select the corners by visual reference to what is displayed in the

> There should be no error generated. d.zoom should always change the region
> extents, but should only do a redraw if there is something to redraw.
> (Although perhaps it does no harm to do a redraw even if there is nothing to
> redraw?). How difficult would it be to have d.zoom work in this way?

Trivial; it's just cleaning up existing functionality.

Actually, I'm wondering if there's even any point to having the rast=
and vector= options and the -j flag. It seems to me that it may as
well always zoom whatever is on the monitor (i.e. -j behaviour). If
you want to zoom a specific map, run d.rast/d.vect first.

Glynn Clements <glynn.clements at virgin.net>

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