[GRASS-dev] Zooming issue in gis manager

Michael Barton michael.barton at asu.edu
Thu Nov 2 00:17:56 EST 2006

You are correct. If -a is not set in g.region it makes small rounding errors
every time you change the region, even if you do not change the resolution
or even if you try to set it explicitly.

Given this, I guess it's better to avoid the small, but annoying rounding
errors of g.region at common map scales than to keep the aligned region
display appearing to be more accurate in less common close-ups of rasters,
especially given that explore mode can be used to produce a display that
correctly matches a region of a few original grid cells in close-ups.

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

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

> From: Maciej Sieczka <tutey at o2.pl>
> Date: Wed, 01 Nov 2006 23:09:56 +0100
> To: grass-dev <grass-dev at grass.itc.it>
> Cc: Michael Barton <michael.barton at asu.edu>
> Subject: Re: [GRASS-dev] Zooming issue in gis manager
> Michael Barton wrote:
>> To clarify a bit...
>> In the "standard" mode, resolution and geometry are preserved by the display
>> in all zooming.
> Michael,
> Not really. The resolution is preserved *only* if -a flag is set in
> g.region call in mapcanvas.tcl, lines 1068/1066. If this -a flag is
> removed, the res is not preserved when you set WIND to match the gis.m
> display (eg. instead of 30 you get 29.56552545). Try to reproduce that,
> can you? And do you confirm my observation or not?
> As to preserving the region extent - this is achieved only if the -a
> flag in question is removed (however, the number of cols on the status
> bar below still doesn't match, interestingly).
> So we can't currently have both: the resolution and the number of rows
> and cols to be preserved when setting WIND to match the gis.m display.
> But we need both. Could we have them?
> Maciek

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