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<p>Black borders are completely expected: reprojection changes the
geometry of the image.</p>
<p>That said, if the area of interest is sufficiently small and the
geometry change being approximatively an affine transformation,
you can try <a class="moz-txt-link-freetext" href="https://gdal.org/programs/gdalmove.html">https://gdal.org/programs/gdalmove.html</a> instead of
gdalwarp to only alter the georeferencing information and not
touch pixel values at all.</p>
<p>Even<br>
</p>
<div class="moz-cite-prefix">Le 18/11/2021 à 15:34, Lorenzo Di
Giacomo a écrit :<br>
</div>
<blockquote type="cite"
cite="mid:CAERmyNRaRCy-xPXy9rDQzykN7oXR_YbGr_pxU_Ja6Y5oZZC8SQ@mail.gmail.com">
<meta http-equiv="content-type" content="text/html; charset=UTF-8">
<div dir="ltr">Hi Carl, thanks for your reply, i noticed that it
happens even if i just reproject the image, without cutting.<br>
Of course the dstalpha works, but it increases the size of the
image and it changes its nature (adding another band) since this
operation is an intermediate operation the resulting image can't
be different from the original, just reporojected.<br>
<br>
<br>
</div>
<br>
<div class="gmail_quote">
<div dir="ltr" class="gmail_attr">Il giorno gio 18 nov 2021 alle
ore 14:11 Carl Godkin <<a href="mailto:cgodkin@gmail.com"
moz-do-not-send="true">cgodkin@gmail.com</a>> ha scritto:<br>
</div>
<blockquote class="gmail_quote" style="margin:0px 0px 0px
0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
<div dir="ltr"> Hi Lorenzo,
<div><br>
</div>
<div>I have faced this and there are two things to consider.</div>
<div><br>
</div>
<div>First, you can specify the georeferenced extents _and_
the SRS of the extents using something like this:</div>
<div><br>
</div>
<div> gdalwarp -t_srs EPSG:3857 \<br>
-te_srs EPSG:4326 -te -109 32 -102 36 \<br>
input.tif output.tif<br>
</div>
<div><br>
</div>
<div>Note that I'm warping to one coordinate system but
trimming based on another one. Is it possible that your
black boundary is due to trimming in the wrong
coordinate system? For instance, if your input map is
projected but the boundary of the map consists of
parallels of latitude or meridians of longitude, then you
could use something like the above. (You can actually get
even fancier by trimming with polygons too; see this
example for inspiration: <a
href="https://gis.stackexchange.com/questions/45053/gdalwarp-cutline-along-with-shapefile"
target="_blank" moz-do-not-send="true">https://gis.stackexchange.com/questions/45053/gdalwarp-cutline-along-with-shapefile</a>
.)</div>
<div><br>
</div>
<div>Second, recognize that the output will always be a
rectangle in the output SRS. If the black border is due
to "no data" areas outside the input map's extent
appearing in the output map, then you can use -dstalpha
("Create an output alpha band to identify nodata
(unset/transparent) pixels.") to mark the output pixels
that shouldn't be part of the map. Basically your black
pixels become transparent in this case.<br>
</div>
<div><br>
</div>
<div>I hope that helps,</div>
<div>carl</div>
<div><br>
</div>
</div>
<br>
<div class="gmail_quote">
<div dir="ltr" class="gmail_attr">On Wed, Nov 17, 2021 at
8:11 AM Lorenzo Di Giacomo <<a
href="mailto:loridigia@gmail.com" target="_blank"
moz-do-not-send="true">loridigia@gmail.com</a>>
wrote:<br>
</div>
<blockquote class="gmail_quote" style="margin:0px 0px 0px
0.8ex;border-left:1px solid
rgb(204,204,204);padding-left:1ex">
<div dir="ltr">Hi all, i have a question, how is it
possible to avoid black borders after reprojection with
"gdal_warp" ? <br>
Basically i have an image that is little rotated, when i
reprojected from 32632 to 4326 the resulting image has
black borders more or less tight depending on the
rotation.<br>
I saw i can change the colors of those no_data (using <span
style="font-variant-ligatures:no-common-ligatures;color:rgb(0,0,0);font-family:Menlo;font-size:11px">-dstnodata)
but how can i do if i dont want it at all? Adding
another band result in a size increase, that i don't
want either.<br>
</span><br>
Thanks !!</div>
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<pre class="moz-signature" cols="72">--
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My software is free, but my time generally not.</pre>
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