[GRASS-dev] suggestion for g.region -a

[Michael Barton]

On Jan 27, 2008, at 11:08 PM, Glynn Clements wrote:

>
> Michael Barton wrote:
>
>> Currently, if you use the -a flag with g.region it will align the
>> region exactly to match the resolution of a map (e.g. g.region -a
>> rast=myrast will set the region to exactly the resolution of myrast
>> regardless of the extents) or the resolution specified in the res or
>> ewres/nwres fields (e.g. g.region -a n=523 s=15 res=10 will adjust
>> the extents a little to make sure the resolution is exactly 10).
>>
>> However, -a is ignored if the map argument (rast=) or resolution
>> arguments are blank.
>
> Actually, you need either vect= or res= (or nsres= or ewres=). rast=
> doesn't have any effect. Also, the interpretation is different for
> vect= compared to the resolution options.
>
>> This means that if you want to change the
>> extents and keep your current resolution, you need to specify the -a
>> flag AND explicitly specify the resolution. Otherwise, the resolution
>> will be adjusted slightly.
>>
>> Could this be modified so that when the -a flag is used and
>> resolution is NOT specified and a map is NOT specified (i.e., only
>> changing extents) it aligns to the current resolution? That is,
>> respect the -a flag when res/ewres/nsres= is blank and rast= is  
>> blank.
>
> It would be possible to implement the -a flag unconditionally,
> although you would need to exclude the cases which already have a
> defined meaning (e.g. "g.region -a nsres=..." only aligns the top and
> bottom edges, leaving the left and right edges unchanged).
>

Yes. That sounds like a good idea.

Michael
____________________
C. Michael Barton, Professor of Anthropology
Director of Graduate Studies
School of Human Evolution & Social Change
Center for Social Dynamics & Complexity
Arizona State University

Phone: 480-965-6262
Fax: 480-965-7671
www: <www.public.asu.edu/~cmbarton>


> -- 
> Glynn Clements <glynn at gclements.plus.com>