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<div class="moz-cite-prefix">Le 08/12/2023 à 20:23, Laurențiu Nicola
via gdal-dev a écrit :<br>
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<div>On Fri, Dec 8, 2023, at 21:11, Even Rouault wrote:<br>
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cite="mid:2d070c43-5426-4ef5-8e31-11b32245020e@app.fastmail.com">
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<div style="font-family:Arial;"> - GeoTIFF DEFLATE 280 MB<br>
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<div>Is it with PREDICTOR=3 ? (If not, then the ZARR datasets
should also be compressed with FILTER=DELTA to have a fair
comparison)<br>
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<div style="font-family:Arial;">I would expect a fair comparison
to be between PREDICTOR=3 and FILTER=DELTA and not the other way
around,</div>
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<p>yes, poor wording of mine. I meant that if using PREDICTOR=3, one
should compare with FILTER=DELTA. But looking more closely, they
are not strictly equivalent. PREDICTOR=3 applies the delta as
b[0]-a[0], b[1]-a[1], b[2]-a[2], b[3]-a[3] where a[0...3] and
b[0...3] are seen as the 4 byte representation of the float32,
whereas FILTER=DELTA does the difference b_float - a_float as
floating point. This isn't the same...</p>
<blockquote type="cite"
cite="mid:99b85735-1176-4a8f-b883-b44176af447c@betaapp.fastmail.com">
<div style="font-family:Arial;"> but it does seem to level the
field significantly:<br>
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<div style="font-family:Arial;"> - GeoTIFF DEFLATE PREDICTOR=3 255
MB<br>
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<div style="font-family:Arial;"> - Zarr DELTA BLOSC zlib NONE 290
MB<br>
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<div style="font-family:Arial;"> - Zarr DELTA BLOSC zlib BIT 266
MB</div>
<div style="font-family:Arial;"> - Zarr DELTA BLOSC zlib BYTE 259
MB</div>
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cite="mid:2d070c43-5426-4ef5-8e31-11b32245020e@app.fastmail.com">
<div style="font-family:Arial;"> - Zarr BLOSC zlib NONE 281 MB<br>
</div>
<div style="font-family:Arial;"> - Zarr BLOSC zlib BIT 253 MB<br>
</div>
<div style="font-family:Arial;"> - Zarr BLOSC zlib BYTE 249 MB<br>
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<div><span style="white-space:pre-wrap;"></span><br>
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<div style="font-family:Arial;">So FILTER=DELTA yields worse
compression, while GeoTIFF PREDICTOR=3 does very well. No need
for Zarr! I don't remember PREDICTOR=3 doing so well in the
past, so.. no idea :-).<br>
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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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