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<p class="MsoNormal"><span style="mso-fareast-language:EN-US">Hi,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="mso-fareast-language:EN-US">The total size of the .tif files in my PROJ_DATA is 959 MB. I tried the LERC compression with MAX_Z_ERROR values 0.001 and 0.01<br>
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<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="mso-fareast-language:EN-US">for /f %i in ('dir /b *.tif') do (gdal_translate -of GTiff -co compress=lerc -co max_z_error=0.001 %i %i.lerc.tif)<br>
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z_error 0.001: 682 MB (-29%)<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="mso-fareast-language:EN-US">z_error 0.01: 549 MB (-43%)<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="mso-fareast-language:EN-US">The savings in space are real (though I think I could save 98 percent of space be deleting the grids which I never use). When it comes to compression/decompression, I think that a proper
test where Proj is used for doing something real would be needed. Does Proj decompress the whole grid file, or just the tiles that it needs? How much time is used for opening the file and finding the tiles?<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="mso-fareast-language:EN-US">-Jukka Rahkonen-<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
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<p class="MsoNormal"><b>Lähettäjä:</b> gdal-dev <gdal-dev-bounces@lists.osgeo.org>
<b>Puolesta </b>Howard Butler via gdal-dev<br>
<b>Lähetetty:</b> sunnuntai 22. joulukuuta 2024 16.39<br>
<b>Vastaanottaja:</b> Even Rouault <even.rouault@spatialys.com><br>
<b>Kopio:</b> gdal dev <gdal-dev@lists.osgeo.org>; proj <proj@lists.osgeo.org><br>
<b>Aihe:</b> Re: [gdal-dev] [PROJ] LIBERTIFF / Thread-safe TIFF reader<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">On Dec 20, 2024, at 4:56 PM, Even Rouault via gdal-dev <<a href="mailto:gdal-dev@lists.osgeo.org">gdal-dev@lists.osgeo.org</a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><span style="font-size:13.5pt;font-family:"Helvetica",sans-serif">Besides reprocessing all of our existing grids,</span><a href="https://github.com/geotiffjs/geotiff.js/tree/master/src/compression"><span style="font-size:13.5pt;font-family:"Helvetica",sans-serif">https://github.com/geotiffjs/geotiff.js/tree/master/src/compression</span></a><span class="apple-converted-space"><span style="font-size:13.5pt;font-family:"Helvetica",sans-serif"> </span></span><span style="font-size:13.5pt;font-family:"Helvetica",sans-serif">seems
to show that it doesn't support ZSTD, which would break at least our wonderful<span class="apple-converted-space"> </span></span><a href="http://cdn.proj.org/"><span style="font-size:13.5pt;font-family:"Helvetica",sans-serif">cdn.proj.org</span></a><span style="font-size:13.5pt;font-family:"Helvetica",sans-serif">interactive
map</span><o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">To throw a wrench into it... <o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">geotiff.js has LERC support. Floating point LERC TIFFs compressed with a MAX_Z_ERROR to one decimal better than the *stated precision* of the grids would be smaller and more efficiently compressed/decompressed. By maybe a 1/3rd over zstd
and deflate.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">See this great write-up by LINZ about the topic <a href="https://github.com/linz/elevation/tree/master/docs/tiff-compression">https://github.com/linz/elevation/tree/master/docs/tiff-compression</a> <o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Howard<o:p></o:p></p>
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