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<p>Giovanni,</p>
<p>gdalwarp takes the absolute value of the second tr value, so -tr
10 -10 is understood as -tr 10 10</p>
<p>It is expected that gdalinfo reports a negative value for the
pixel size factor for the vertical axis, as in GeoTIFF when the
image is north-up, the first line of the image is intended to be
the one displayed at the top of your screen, and as the line
number of your screen increase from the top of your screen to the
bottom, northings or latitudes increase from the bottom to the
top, hence the negative sign...</p>
<p>More detailed equivalent explanation at
<a class="moz-txt-link-freetext" href="https://gis.stackexchange.com/a/229807/218992">https://gis.stackexchange.com/a/229807/218992</a> (you can ignore the
paragraph "As to why the image flipped..." which is specific to
the question in that stackexchange thread)<br>
</p>
<p>Even<br>
</p>
<div class="moz-cite-prefix">Le 19/11/2023 à 02:15, Giovanni
Anconitano via gdal-dev a écrit :<br>
</div>
<blockquote type="cite"
cite="mid:CADpTLOmJ9mNDPG4Ht4_OoFEXLxATtiVhnbNv+miNeGC+1iKkBg@mail.gmail.com">
<meta http-equiv="content-type" content="text/html; charset=UTF-8">
<div dir="ltr">Hello,<br>
<br>
I have a question about how to properly set the -tr flag when
using gdalwarp.<br>
In particular, I'm using gdalwarp for resampling a GeoTiff from
its original resolution to a target resolution. <br>
Let's consider, for simplicity, the original pixel size equal to
(5m, 5m) and the target resolution equal to (10m, 10m).<br>
<br>
This is the command I use: gdalwarp -tr 10 -10 input.tif
output.tif<br>
<br>
I'm using a negative <yres> because when I open the
GeoTiff file in QGIS, or if I use gdalinfo, I get a pixel size
equal to (5, -5) for the source raster.<br>
<br>
Is it correct to use a negative <yres> with gdalwarp? I
also tried -tr 10 10, but the result seems to be the same as the
case in which I use -tr 10 -10.<br>
In both cases gdalinfo and QGIS display (10,-10) as the pixel
size.<br>
<br>
How does gdalwarp treat a negative yres value?<br>
<br>
<div>Thank you</div>
<div><br>
</div>
<div>Giovanni<br>
</div>
</div>
<br>
<div
style="font-size:small;font-family:arial;background-color:rgb(255,255,255)"><span><span><span><span></span></span></span></span><b>
<div><font color="#ff0000"><b>Fai crescere le giovani
ricercatrici e i giovani ricercatori</b><br>
</font></div>
</b>
<div><b><font color="#ff0000">con il 5 per mille alla Sapienza</font><br>
</b>
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<div>Scrivi il codice fiscale
dell'Università <b>80209930587<br>
<a
href="https://www.uniroma1.it/it/node/23149" target="_blank"
moz-do-not-send="true">Cinque
per mille</a></b></div>
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My software is free, but my time generally not.</pre>
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