<div dir="ltr">The problem is that I don't know want an alpha channel because some of my users work on MapInfo and MapInfo doesn't deal with alpha channels..</div><div class="gmail_extra"><br><div class="gmail_quote">2015-01-14 11:39 GMT+01:00 Even Rouault-2 [via OSGeo.org] <span dir="ltr"><<a href="/user/SendEmail.jtp?type=node&node=5181437&i=0" target="_top" rel="nofollow" link="external">[hidden email]</a>></span>:<br><blockquote style='border-left:2px solid #CCCCCC;padding:0 1em' class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><span class="">
Mathieu,
<br><br>If 0 is a valid value at some locations of your raster, then you cannot use it
<br>as the nodata value. Use an alpha band instead for example by using -dstalpha
<br>instead of -dstnodata 0
<br><br>Even
<br></span><div><div class="h5"><div><div class='shrinkable-quote'><br>> Hello,
<br>>
<br>> I crop a 3 band raster by a polygon with the following formula :
<br>> /gdalwarp -of GTiff -cutline polygon.shp -cl polygon input.tif output.tif
<br>> /
<br>> But pixels outside my polygon are assigned the 0 value. I'd like them to
<br>> have nodata
<br>>
<br>> If I put the -dstnodata 0 option :
<br>> /gdalwarp -of GTiff -cutline polygon.shp -cl polygon input.tif output.tif
<br>> -dstnodata 0/, all the pixels in each of the 3 bands that contain the 0
<br>> value will be turned to nodata, even if they are contained in my polygon.
<br>>
<br>> Hence, 127 0 222 will become 127 nodata 222
<br>> or 0 127 222 will become nodata 127 222
<br>>
<br>> How to put the nodata value only outside my polygon ?
<br>>
<br>> Thanks a lot in advance !
<br>>
<br>> Mathieu
<br>>
<br>>
<br>>
<br>> --
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