<div dir="ltr"><div><div><div>Even,<br><br></div>Many thanks! This did fix the issue.<br>Agreed, having both nodata and transparency would confuse things, and I see that this way also ensures that it works well with cropped maps with pure black pixels.<br><br></div>Best regards,<br><br></div>Tim<br><div><div><br><br></div></div></div><div class="gmail_extra"><br><div class="gmail_quote">On 5 October 2017 at 22:21, Even Rouault <span dir="ltr"><<a href="mailto:even.rouault@spatialys.com" target="_blank">even.rouault@spatialys.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><u></u>
<div style="font-family:'monospace';font-size:9pt;font-weight:400;font-style:normal"><div><div class="h5">
<p style="margin-top:0px;margin-bottom:0px;margin-left:0px;margin-right:0px;text-indent:0px">On jeudi 5 octobre 2017 18:46:32 CEST Tim Waters wrote:</p>
<p style="margin-top:0px;margin-bottom:0px;margin-left:0px;margin-right:0px;text-indent:0px">> Hello,</p>
<p style="margin-top:0px;margin-bottom:0px;margin-left:0px;margin-right:0px;text-indent:0px">> </p>
<p style="margin-top:0px;margin-bottom:0px;margin-left:0px;margin-right:0px;text-indent:0px">> I'm seeing an issue which is present in 2.2.2 (tags/2.2.2 from github) and</p>
<p style="margin-top:0px;margin-bottom:0px;margin-left:0px;margin-right:0px;text-indent:0px">> seen in 1.11.3 (Ubuntu 16.04) but not present in 1.10.1 (Ubuntu 14.04).</p>
<p style="margin-top:0px;margin-bottom:0px;margin-left:0px;margin-right:0px;text-indent:0px">> </p>
<p style="margin-top:0px;margin-bottom:0px;margin-left:0px;margin-right:0px;text-indent:0px">> If a raster with an alpha channel has nodata set, and overviews via</p>
<p style="margin-top:0px;margin-bottom:0px;margin-left:0px;margin-right:0px;text-indent:0px">> gdaladdo are created, the overviews use the nodata value for the value of</p>
<p style="margin-top:0px;margin-bottom:0px;margin-left:0px;margin-right:0px;text-indent:0px">> the alpha channel. However, using the nearest resampling method correctly</p>
<p style="margin-top:0px;margin-bottom:0px;margin-left:0px;margin-right:0px;text-indent:0px">> sets the alpha to zero. All other resampling methods except nearest seem to</p>
<p style="margin-top:0px;margin-bottom:0px;margin-left:0px;margin-right:0px;text-indent:0px">> give the same wrong result.</p>
<p style="margin-top:0px;margin-bottom:0px;margin-left:0px;margin-right:0px;text-indent:0px">> </p>
<p style="margin-top:0px;margin-bottom:0px;margin-left:0px;margin-right:0px;text-indent:0px">> I've created a repository with all the files and readme containing the</p>
<p style="margin-top:0px;margin-bottom:0px;margin-left:0px;margin-right:0px;text-indent:0px">> workflow.</p>
<p style="margin-top:0px;margin-bottom:0px;margin-left:0px;margin-right:0px;text-indent:0px">> <a href="https://github.com/timwaters/gdal_gdaladdo_issue" target="_blank">https://github.com/timwaters/<wbr>gdal_gdaladdo_issue</a> with screenshots of the</p>
<p style="margin-top:0px;margin-bottom:0px;margin-left:0px;margin-right:0px;text-indent:0px">> expected and observed files opened in Gimp to view the pixel values.</p>
<p style="margin-top:0px;margin-bottom:0px;margin-left:0px;margin-right:0px;text-indent:0px">> </p>
<p style="margin-top:0px;margin-bottom:0px;margin-left:0px;margin-right:0px;text-indent:0px">> The use case is <a href="http://mapwarper.net" target="_blank">mapwarper.net</a> where users upload ungeoreferenced images,</p>
<p style="margin-top:0px;margin-bottom:0px;margin-left:0px;margin-right:0px;text-indent:0px">> they get converted to tifs and have overviews added, then they can mask</p>
<p style="margin-top:0px;margin-bottom:0px;margin-left:0px;margin-right:0px;text-indent:0px">> them (gdal_rasterize) and then warp the masked files, with overviews added</p>
<p style="margin-top:0px;margin-bottom:0px;margin-left:0px;margin-right:0px;text-indent:0px">> finally. I'm updating the server to run on Ubuntu 16.04 and will have to</p>
<p style="margin-top:0px;margin-bottom:0px;margin-left:0px;margin-right:0px;text-indent:0px">> compile gdal.</p>
<p style="margin-top:0px;margin-bottom:0px;margin-left:0px;margin-right:0px;text-indent:0px">> </p>
<p style="margin-top:0px;margin-bottom:0px;margin-left:0px;margin-right:0px;text-indent:0px">> Flow is:</p>
<p style="margin-top:0px;margin-bottom:0px;margin-left:0px;margin-right:0px;text-indent:0px">> </p>
<p style="margin-top:0px;margin-bottom:0px;margin-left:0px;margin-right:0px;text-indent:0px">> #Apply overviews to ungeoreferenced raster</p>
<p style="margin-top:0px;margin-bottom:0px;margin-left:0px;margin-right:0px;text-indent:0px">> gdaladdo -r average treasure_island.tif 2 4 8 16</p>
<p style="margin-top:0px;margin-bottom:0px;margin-left:0px;margin-right:0px;text-indent:0px">> </p>
<p style="margin-top:0px;margin-bottom:0px;margin-left:0px;margin-right:0px;text-indent:0px">> #Rasterise ungeoreferenced raster with the cropping mask</p>
<p style="margin-top:0px;margin-bottom:0px;margin-left:0px;margin-right:0px;text-indent:0px">> gdal_rasterize -i -b 1 -b 2 -b 3 -burn 17 -burn 17 -burn 17 20.gml -l</p>
<p style="margin-top:0px;margin-bottom:0px;margin-left:0px;margin-right:0px;text-indent:0px">> features treasure_island.tif</p>
<p style="margin-top:0px;margin-bottom:0px;margin-left:0px;margin-right:0px;text-indent:0px">> </p>
<p style="margin-top:0px;margin-bottom:0px;margin-left:0px;margin-right:0px;text-indent:0px">> #Georeference & warp the raster</p>
<p style="margin-top:0px;margin-bottom:0px;margin-left:0px;margin-right:0px;text-indent:0px">> gdal_translate -a_srs '+init=epsg:4326' -of VRT treasure_island.tif</p>
<p style="margin-top:0px;margin-bottom:0px;margin-left:0px;margin-right:0px;text-indent:0px">> temp.vrt -gcp 100.38, 83.096, -122.377, 37.830 -gcp 430.1966, 370.08,</p>
<p style="margin-top:0px;margin-bottom:0px;margin-left:0px;margin-right:0px;text-indent:0px">> -122.363, 37.8207 -gcp 313.69, 61.68, -122.368, 37.831</p>
<p style="margin-top:0px;margin-bottom:0px;margin-left:0px;margin-right:0px;text-indent:0px"> </p>
<p style="margin-top:0px;margin-bottom:0px;margin-left:0px;margin-right:0px;text-indent:0px"> </p>
<p style="margin-top:0px;margin-bottom:0px;margin-left:0px;margin-right:0px;text-indent:0px">> gdalwarp -rn -dstalpha -srcnodata '17 17 17' -s_srs 'EPSG:4326' temp.vrt</p>
<p style="margin-top:0px;margin-bottom:0px;margin-left:0px;margin-right:0px;text-indent:0px">> treasure_island_warped.tif -co TILED=YES -co COMPRESS=LZW</p>
<p style="margin-top:0px;margin-bottom:0px;margin-left:0px;margin-right:0px;text-indent:0px"> </p>
</div></div><p style="margin-top:0px;margin-bottom:0px;margin-left:0px;margin-right:0px;text-indent:0px">Tim,</p>
<p style="margin-top:0px;margin-bottom:0px;margin-left:0px;margin-right:0px;text-indent:0px"> </p>
<p style="margin-top:0px;margin-bottom:0px;margin-left:0px;margin-right:0px;text-indent:0px">The issue come from the above step. Basically this will add an alpha channel and also set implicitly a dest nodata value to 17. In GDAL extended TIFF, the nodata value applies to all channels. But when you have an alpha channel, having nodata values in addition doesn't really make sense and just confuse everything afterwards.</p>
<p style="margin-top:0px;margin-bottom:0px;margin-left:0px;margin-right:0px;text-indent:0px">If you add -dstnodata none, this will fix the issue.</p>
<p style="margin-top:0px;margin-bottom:0px;margin-left:0px;margin-right:0px;text-indent:0px">I think we should probably default to this behaviour when -dstalpha is specified.</p>
<p style="margin-top:0px;margin-bottom:0px;margin-left:0px;margin-right:0px;text-indent:0px"> </p>
<p style="margin-top:0px;margin-bottom:0px;margin-left:0px;margin-right:0px;text-indent:0px">Even</p>
<p style="margin-top:0px;margin-bottom:0px;margin-left:0px;margin-right:0px;text-indent:0px"> </p>
<p style="margin-top:0px;margin-bottom:0px;margin-left:0px;margin-right:0px;text-indent:0px">-- </p>
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