[GRASS-dev] Zooming issue in gis manager

Michael Barton michael.barton at asu.edu
Wed Nov 1 09:59:53 EST 2006

This sounds like there is no good reason to set this for interactive zooming
by default. If someone wants to use this feature, they could explicitly set
it in g.region.

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: Glynn Clements <glynn at gclements.plus.com>
> Date: Wed, 1 Nov 2006 06:38:55 +0000
> To: Michael Barton <michael.barton at asu.edu>
> Cc: grass-dev <grass-dev at grass.itc.it>
> Subject: Re: [GRASS-dev] Zooming issue in gis manager
> Michael Barton wrote:
>> The reported problem with displaying grid cells at high magnification is
>> primarily or entirely a function of how g.region -a aligns the region with
>> the raster grid cell boundaries. I don't know how this works internally and
>> someone with C programming experience will have to deal with it if we want
>> it to work differently
> window.ns_res = x;
> window.ew_res = x;
> if (flag.res_set->answer) {
> window.north =  ceil(window.north/x) * x ;
> window.south = floor(window.south/x) * x ;
> window.east = ceil(window.east/x) * x ;
> window.west = floor(window.west/x) * x ;
>                 }
> IOW, it essentially shifts the cell grid such that the origin of the
> coordinate system lies on the intersection between four cells.
> Given that the origin for most coordinate systems is a completely
> arbitrary location arising from various completely arbitrary constants
> (e.g. whichever round numbers where chosen as the false easting and
> northing), I have no idea what the intended purpose of the -a flag is,
> but I'm fairly sure that it shouldn't be used by default.
> -- 
> Glynn Clements <glynn at gclements.plus.com>

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