[GRASSLIST:10373] Re: [GRASS5] New release candidate 3 of GIS Manager 2

[Maciek Sieczka]

On Wed, 15 Feb 2006 16:59:15 -0700
Michael Barton <michael.barton at asu.edu> wrote:

Michael,

> Maciek,
> 
> I see what you are talking about. But the GIS Manager is NOT doing
> this. The zooming in the new GIS Manager does NOT use d.zoom.

I know. I'm not saying it is. But I'm wondering if gis.m could follow
it, as it is doing the good thing (except
https://intevation.de/rt/webrt?serial_num=3961, but this is another
story).

> It simply resets the region extents--extents ONLY--by issuing a
> g.region n=y1 s=y2 e=x1 w=x2 (no change to resolution)
> 
> I tried adding the -a flag and it makes no difference. 

When you need to preserve resolution, but the given extents would not
let you to, you need to specify the input resolution explicitely, which
you want to be preserved after g.region:


### The initial region:

$ g.region -p
projection: 1 (UTM)
zone:       33
datum:      wgs84
ellipsoid:  wgs84
north:      5679546
south:      5678732
west:       598654
east:       599761
nsres:      1
ewres:      1
rows:       814
cols:       1107

### Let's zoom out - not preserving the res, like gis.m does it (bad):

$ g.region n=5680762.10112026 s=5677880.44652981 w=598415.29951403
e=600978.962345 -p projection: 1 (UTM)
zone:       33
datum:      wgs84
ellipsoid:  wgs84
north:      5680762.10112026
south:      5677880.44652981
west:       598415.29951403
east:       600978.962345
nsres:      0.99988015
ewres:      0.9998685
rows:       2882
cols:       2564

### And now zoom out preserving the res, like d.zoom does it (good):

$ g.region n=5680762.10112026 s=5677880.44652981 w=598415.29951403
e=600978.962345 res=1 -ap projection: 1 (UTM)
zone:       33
datum:      wgs84
ellipsoid:  wgs84
north:      5680763
south:      5677880
west:       598415
east:       600979
nsres:      1
ewres:      1
rows:       2883
cols:       2564


> It looks like it is some kind of a rounding issue in g.region (or
> possibly in the OS).

I guess it's not. Simply g.region does exactly what you are telling it
to do. Maybe telling it to preserve the input res then would be all that
we need.

> In a working context the change is a tiny fraction of a mm in
> your example below. So it wouldn't make any meaningful difference in
> most cases.

It's not about millimeters during display or else. It's about preserving
the current resolution when zooming. This is a must I believe. You can't
let your zooming tool to change the working region resolution. Why
should you?

> However, it is odd that it happens. Maybe someone who
> understands the g.region code can explain it.

I hope so to. I know what I'm seeing only.

Maciek

--------------------
W polskim Internecie s? setki milion?w stron. My przekazujemy Tobie tylko najlepsze z nich!
http://katalog.panoramainternetu.pl/