[GRASS-user] Region definition in Grass 6.1 (and 6.1 cvs)

[Michael Barton]

Glynn et al,


> 
>>> - region matches display (cut region at nearest cell boundary)
>> 
>> Region for non-display modules matches the region set for rendering a map to
>> the current display. This is pretty much how things work in normal mode if
>> run from the GIS Manager menus.
> 
> The problem is that, when you have multiple displays, it's likely to
> be unclear as to which one determines the region used by non-display
> commands.

The fundamental issue is that in GRASS, the region setting constrains the
actions of modules that modify maps. This is different from at least some
other programs and can be either very useful or an annoyance (depending on
the time of day). The 2nd issue is that zooming/unzooming and panning in the
display requires changing the region extents.

Given that the display is setting the extents but should not set the
resolution (see below), the question is whether interactively
zooming/panning in the display should also set the region extents for
non-display commands or not. Having an option to turn this on or off is
desirable, but seems difficult to code given the underlying architecture (or
at least seems difficult on a Monday morning).

> 
> Also, requiring the region to match one of the displays is problematic
> if you are working at a relatively high resolution. You don't want to
> have to force the displays to operate at that resolution simply
> because you cannot make a command use a resolution which doesn't match
> a display.

For best performance, the display resolution should work the way Cedric set
up explore mode--that is it should always produce a constant number of
pixels that is proportional to the display size.

But this should have nothing to do with the resolution used by GIS modules
that perform actions on maps. This resolution should be set explicitly by
the user.

Again, coding this so that the display changes the region resolution for
itself but for nothing else seems complicated to implement, though
desirable.


Michael

__________________________________________
Michael Barton, Professor of Anthropology
School of Human Evolution & Social Change
Center for Social Dynamics and Complexity
Arizona State University

phone: 480-965-6213
fax: 480-965-7671
www: http://www.public.asu.edu/~cmbarton