[GRASS-user] Invalid region and coordinates when trying to reproject.

[Marcello Gorini]

Thanks for the suggestions.

Markus:

> Please post
> g.proj -p

-PROJ_INFO--------------------
-----------------------------
name       : Mercator
proj       : merc
datum      : wgs84
ellps      : wgs84
lon_0      : 0
k          : 1
x_0        : 0
y_0        : 0
no_defs    : defined
-PROJ_UNITS------------------------------------------------
unit       : metre
units      : metres
meters     : 1

Doesn't seem to have a problem, does it?

Now I looked at the revised wiki (thanks Hamish) and followed it entirely.

It worked. I guess either I hadn't followed everything the last time or
this r.region part was
really needed.

OK, but I have another problem.

When I first imported the data to the latlog location, besides being
flipped, it appeared stretched in the N-S direction.
When I fixed it with region w=-180 e=180, everything fell back to its
correct place and it was fine, with no more stretching.

Now, when I reprojected it, it is stretched again.

Doing g.region in my latlong location, I get a resolution of 5 minutes with
rows=2159 cols=4321.
When I r.proj -g in the mercator location, following Hamish suggestion, I
get
Input Projection Parameters:  +proj=longlat +no_defs +a=6378137
+rf=298.257223563 +towgs84=0.000,0.000,0.000
Input Unit Factor: 1
Output Projection Parameters:  +proj=merc +lon_0=0 +k=1 +x_0=0 +y_0=0
+no_defs +a=6378137 +rf=298.257223563 +towgs84=0.000,0.000,0.000
Output Unit Factor: 1
Input map <rbd at ATLANTIC> in location <GEBCO_GEODETIC>:
n=46050366.66617828 s=-46050366.66617872 w=-20028233.86541469
e=20028233.86541469 rows=2159 cols=4321

But when I apply the n-s w-e it suggests and r.proj again:

Input:
Cols: 4321 (4321)
Rows: 2159 (2159)
North: 89.916705 (89.916705)
South: -89.916705 (-89.916705)
West: -179.916686 (-179.916686)
East: 179.916686 (179.916686)
EW-res: 0.083275
NS-res: 0.083295

Output:
Cols: 4321 (4321)
Rows: 2159 (2159)
North: 46050366.666178 (46050366.666178)
South: -46050366.666179 (-46050366.666179)
West: -20028233.865415 (-20028233.865415)
East: 20028233.865415 (20028233.865415)
EW-res: 9270.184617
NS-res: 42658.977921


You see? It stretched the NS-res. Is it me or the data? (probably me, of
course).

Thanks again,
Marcello.


On Mon, Jul 2, 2012 at 2:47 AM, Hamish <hamish_b at yahoo.com> wrote:

> Markus:
> > ...
> > >  |
> >    Projection: x,y
> >
> > ... this looks suspicious! Above output may help us to find
> > the problem.
>
> probably he was following my tutorial at
>  http://grass.osgeo.org/wiki/Global_datasets#ETOPO1_.28DEM.29
>
> which uses a nasty hack to get around the original grid-registered
> data exceeding the limits of polar coordinate space:
> r.in.bin -f in=etopo1_bed_g.flt out=etopo1_bed_g \
>    n=90.008333333335 s=-90.008333333335 e=180.00833333334 \
>    w=-180.00833333334 rows=10801 cols=21601 anull=-9999
>
> but the cellhd/ file was not reset in sync with the location.
>
> I have now rewriten that wiki entry to use a r.region cleanup
> method instead of ugly filesystem edits.
>
>
> Hamish
>
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