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Hi,<br>
Why... I am not sure. You could always use the -tr xres yres switch
in gdalwarp.<br>
<br>
<a class="moz-txt-link-freetext" href="http://www.geos.ed.ac.uk/~smudd/TopoTutorials/html/tutorial_raster_conversion.html" target="_top" rel="nofollow" link="external">http://www.geos.ed.ac.uk/~smudd/TopoTutorials/html/tutorial_raster_conversion.html</a><br>
<br>
-tr will set the pixel size. (ex -tr 200 200) I don't think it work
with gdal_translate (clipper) yet. (Needs gdal version2)
<a class="moz-txt-link-freetext" href="http://www.gdal.org/gdal_translate.html" target="_top" rel="nofollow" link="external">http://www.gdal.org/gdal_translate.html</a><br>
<br>
Should work.<br>
Nicolas<br>
<br>
<br>
<div class="moz-cite-prefix">Le 2015-05-19 21:12, Luciano La Sala
[via OSGeo.org] a écrit :<br>
</div>
<blockquote style='border-left:2px solid #CCCCCC;padding:0 1em' cite="mid:555BE012.4070709@yahoo.com.ar" type="cite">
Dear QGIS users,
<br>
<br>
I am using QGIS V 2.2.0 (OS-Windows 8), and need to prepare raster
files <br>
(ESRI ArcInfo Grids) to be later used in a species distribucion
model <br>
using MaxEnt. Each of the original raster files (environmental
variables <br>
for Guadalquivir, Spain) has a different spatial extension (but
all <br>
share the same pixel size of 200, -200). However, to be able to
use <br>
these layers in MaxEnt, all of them need to have the exact same
spatial <br>
extent. Therefore, I clipped every raster using a polygon of <br>
Guadalquivir. After clipping, I save as GeoTIFF but the new
rasters have <br>
their original pixel size (200,-200) slightly altered <br>
(200.001,-199.942). I wouldn't bother too much about this menial <br>
difference in cell size if it weren't for the warning message that
I get <br>
(see below) when trying to convert the GeoTIFF rasters to ASCII (a
<br>
requirement for MaxEnt to work):
<br>
<br>
Warning 1: Producing a Golden Surfer style file with DX and DY
instead
<br>
of CELLSIZE since the input pixels are non-square. Use the
<br>
FORCE_CELLSIZE=TRUE creation option to force use of DX for
<br>
even though this will be distorted. Most ASCII Grid readers
<br>
(ArcGIS included) do not support the DX and DY parameters. .
<br>
<br>
The Layer Spatial Reference System for Guadalquivir is:
<br>
<br>
+proj=utm +zone=30 +ellps=GRS80 +towgs84=0,0,0,0,0,0,0 +units=m
+no_defs <br>
<br>
<br>
The Layer Spatial Reference System for the raster layers is:
<br>
<br>
+proj=utm +zone=30 +ellps=GRS80 +units=m +no_defs
<br>
<br>
When clipping, I'm using the function raster >> Extraction
>> Clipper <br>
followed by the options...
<br>
<br>
No data value = 0
<br>
Mask layer: Guadalquivir
<br>
Following, I save the new raster as GeoTIFF.
<br>
<br>
Questions:
<br>
<br>
Should the clipping be done using a polygon with the exact same <br>
projection? I am not sure to what extent the projections differ
between <br>
the layers above.
<br>
<br>
In case response to question is "Yes" (same projections needed), I
did <br>
the clipping using both options: first by saving Guadalquivir as
.shp <br>
with the raster's projection, and later the other way around, that
is <br>
saving raster files with Guadalquivir's projection. Regardless of
the <br>
option, pixel size remains altered/uneven.
<br>
<br>
How can I keep the original pixel size of 200,-200?
<br>
<br>
Thank you in advance.
<br>
<br>
Luciano
<br>
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