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gdalwarper.cpp: more details about OPTIMIZE_SIZE #10817

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Sep 18, 2024
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gdalwarper.cpp: more details about OPTIMIZE_SIZE #10817

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20 changes: 19 additions & 1 deletion alg/gdalwarper.cpp
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Expand Up @@ -1167,6 +1167,20 @@ CPLErr GDALWarpDstAlphaMasker(void *pMaskFuncArg, int nBandCount,
* will be selected, not just those whose center point falls within the
* polygon.</li>
*
* <li>XSCALE: Ratio expressing the resampling factor (number of destination
* pixels per source pixel) along the target horizontal axis.
* The scale is used to determine the number of source pixels along the x-axis
* that are considered by the resampling algorithm.
* Equals to one for no resampling, below one for downsampling
* and above one for upsampling. This is automatically computed, for each
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* processing chunk, and may thus vary among them, depending on the
* shape of output regions vs input regions. Such variations can be undesired
* in some situations. If the resampling factor can be considered as constant
* over the warped area, setting a constant value can lead to more reproducible
* pixel output.</li>
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Describe XSCALE=FROM_GRID_SAMPLING ?

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Let's keep it as undocumented for now / implementation detail... (partly because I'm never satisfied with those settings, and also because this is tricky to describe accurately and in a understandable way)

*
* <li>YSCALE: Same as XSCALE, but along the horizontal axis.</li>
*
* <li>OPTIMIZE_SIZE: This defaults to FALSE, but may be set to TRUE
* typically when writing to a compressed dataset (GeoTIFF with
* COMPRESS creation option set for example) for achieving a smaller
Expand All @@ -1176,7 +1190,11 @@ CPLErr GDALWarpDstAlphaMasker(void *pMaskFuncArg, int nBandCount,
* of the file. However sticking to target block size may cause major
* processing slowdown for some particular reprojections. Starting
* with GDAL 3.8, OPTIMIZE_SIZE mode is automatically enabled when it is safe
* to do so.</li>
* to do so.
* As this parameter influences the shape of warping chunk, and by default the
* XSCALE and YSCALE parameters are computed per warping chunk, this parameter may
* influence the pixel output.
* </li>
*
* <li>NUM_THREADS: (GDAL >= 1.10) Can be set to a numeric value or ALL_CPUS to
* set the number of threads to use to parallelize the computation part of the
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1 change: 1 addition & 0 deletions doc/source/spelling_wordlist.txt
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Expand Up @@ -3360,6 +3360,7 @@ UpdateFeature
updateTime
UpperLeftX
UpperLeftY
upsampling
upsert
uri
url
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