Details Ticket 4438


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Serial Number 4438
Subject export of AAIGrid and arc incorrect
Area grass6
Queue grass
Requestors wegmann@biozentrum.uni-wuerzburg.de
Owner fwarmerdam
Status resolved
Last User Contact Sat May 12 17:54:58 2007 (1 yr ago)
Current Priority 30
Final Priority 70
Due No date assigned
Last Action Sat May 12 17:54:58 2007 (1 yr ago)
Created Tue May 9 14:20:55 2006 (2 yr ago)

Transaction History Ticket 4438


Tue, May 9 2006 14:20:55    Request created by guest  
Subject: export of AAIGrid and arc incorrect

Platform: GNU/Linux/x86
grass binary for platform: Compiled from Sources
GRASS Version: cvs 08.05.2006

Hello, 

concerning the export of AAIGrid (r.out.gdal) and ArcInfo Ascii Grid 
(r.out.arc) an incorrect output occurs if the nsres/ewres in GRASS is not 
equal - AAIGrid/arc stores only one value for res. 

The difference between the resolutions is (in my case) small (3-> decimal 
place) hence the incorrect export is only visible if high numbers of row/col
exist (high resolution imagery/covering continental scales). 

The remedy is to resample the image to an equal nsres ewres. The problem is 
located in the data format and not GRASS so I would suggest to either

1. prompt a warning if nsres != ewres

or

2. do an automatic resampling with equal nsres/ewres with an info prompt

otherwise the exported files have a wrong geolocation.

regards, Martin



Tue, May 9 2006 16:40:05    Taken by fwarmerdam  
Tue, May 9 2006 16:41:10    Comments added by fwarmerdam  
I will ensure that the AAIGRID driver issues a warning message if the
geotransform cannot be properly represented (non-square pixels).  I think
resampling on the fly would not be in the spirit of an exporter. 
Tue, May 9 2006 16:44:46    Comments added by guest  
It seems that for GDAL 1.3.2 support was added to the AAIGRID
driver to use DX and DY keywords instead of CELLSIZE if these don't
agree.  This is a "Golden Surfer" convention and may make the file 
unreadable for ArcGrid, I'm not exactly sure.  But there is no clear
need for a warning any more. 

Sun, Jun 11 2006 14:10:29    Mail sent by msieczka  
What is the status? The most recent information is too unclear for me, sorry.
Maciek
Sat, Nov 25 2006 11:18:44    Mail sent by mneteler  
Martin,

can you please try again with r.out.gdal2? r.out.gdal was rewritten in GRASS
6.3 as C implementation (currently named r.out.gdal2).

Markus
Wed, Nov 29 2006 13:40:33    Mail sent by wegmann@biozentrum.uni-wuerzburg.de  
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Reply-To wegmann@biozentrum.uni-wuerzburg.de
To grass-bugs@intevation.de
Subject Re: [bug #4438] (grass) export of AAIGrid and arc incorrect
Date Wed, 29 Nov 2006 13:40:01 +0100
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Hello,=20

I am not totally sure if it works correct - import and export of the same=20
image works fine but doing resampling inbetween produces a shift in the=20
exported file.

I'll try to locate the error (gdal or elsewhere) and post to grass-bugs.

Martin

On Saturday 25 November 2006 11:18, Markus Neteler via RT wrote:
> Martin,
>
> can you please try again with r.out.gdal2? r.out.gdal was rewritten in
> GRASS 6.3 as C implementation (currently named r.out.gdal2).
>
> Markus
>
> -------------------------------------------- Managed by Request Tracker

=2D-=20
Martin Wegmann

DLR - German Aerospace Center
German Remote Sensing Data Center
@
Dept.of Geography
Remote Sensing and Biodiversity Unit
&&
Dept. of Animal Ecology and Tropical Biology
University of Wuerzburg
Am Hubland
97074 W=FCrzburg

phone: +49-(0)931 - 888 4797
mobile: +49-(0)175 2091725
fax:   +49-(0)931 - 888 4961
http://www.biota-africa.org
http://www.biogis.de


Sat, May 12 2007 17:54:58    Status changed to resolved by mneteler  
Sat, May 12 2007 17:54:58    Mail sent by mneteler  
Martin,

now r.out.gdal is a real C implementation in GRASS 6.3. Can you please try and
let us know if the problem persists? On the other hand, it would be a GDAL
problem then (to be reported there). I take liberty to close the report.

Markus
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