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<p style="margin-top:0;margin-bottom:0">Yes, you're right, I may need some extra pixels on the boundaries (depend on the resampling method).</p>
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<p style="margin-top:0;margin-bottom:0">Does not GDAL manage this by itself ? I mean, if you ask for a warp, it doesn't read all necessary pixel to do the resampling ?</p>
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<p style="margin-top:0;margin-bottom:0">Since GDAL 2.0, there is some API changes, and I'm looking for the most efficient way to do my operation : extract a region specified with geographic coordinates (in the same SRS as the data source) to a fixed size pixel
buffer. Resampling should occur because the pixel count of the extracted region (source) and pixel count of the buffer (destination) will not fit.</p>
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<div id="divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" style="font-size:11pt" color="#000000"><b>De :</b> gdal-dev <gdal-dev-bounces@lists.osgeo.org> de la part de Joaquim Manuel Freire Luís <jluis@ualg.pt><br>
<b>Envoyé :</b> jeudi 11 octobre 2018 16:47:27<br>
<b>À :</b> gdal-dev@lists.osgeo.org<br>
<b>Objet :</b> Re: [gdal-dev] Best method to extract regions from a raster into a memory buffer</font>
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<p class="x_MsoNormal"><span lang="EN-US" style="">Hi,</span></p>
<p class="x_MsoNormal"><span lang="EN-US" style=""> </span></p>
<p class="x_MsoNormal"><span lang="EN-US" style="">I think you need an extra point. If you will be doing resampling than you need extra row/columns for the boundary conditions (one for linear, two for spline/bicubic). Regarding 2) the options are: round to
closest node, or to the inner or to the outer node.</span></p>
<p class="x_MsoNormal"><span lang="EN-US" style=""> </span></p>
<p class="x_MsoNormal"><span lang="EN-US" style="">Joaquim</span></p>
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<p class="x_MsoNormal"><b><span lang="EN-US">From:</span></b><span lang="EN-US"> gdal-dev <gdal-dev-bounces@lists.osgeo.org>
<b>On Behalf Of </b>Aurélien Albert<br>
<b>Sent:</b> Thursday, October 11, 2018 11:28 AM<br>
<b>To:</b> gdal-dev@lists.osgeo.org<br>
<b>Subject:</b> [gdal-dev] Best method to extract regions from a raster into a memory buffer</span></p>
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<p><span style="font-size:12.0pt; color:black">Hi,</span></p>
<p><span style="font-size:12.0pt; color:black"> </span></p>
<p><span style="font-size:12.0pt; color:black">I'm doing C++ applications and I'm familiar with GDAL 1.7 C/C++ API. For a new application, I'm switching to GDAL 2.2.</span></p>
<p><span style="font-size:12.0pt; color:black">In this application, I have the need to extract a region from a raster :</span></p>
<p><span style="font-size:12.0pt; color:black"> </span></p>
<p><span style="font-size:12.0pt; color:black">Let's say I have 4000px x 4000px elevation raster, covering the whole earth, in EPSG 4326.</span></p>
<p><span style="font-size:12.0pt; color:black">Now I want to extract the rectangle region between two points (lat_1/long_1) and (lat_2/long_2) in a 128px x 128px tile.</span></p>
<p><span style="font-size:12.0pt; color:black">I don't want to extract this region in a file, but in memory, to create a data buffer and then work on this buffer with my application.</span></p>
<p><span style="font-size:12.0pt; color:black"> </span></p>
<p><span style="font-size:12.0pt; color:black">Which is the best/more performant way to do this ?</span></p>
<p><span style="font-size:12.0pt; color:black"> </span></p>
<p><span style="font-size:12.0pt; color:black">Knowing that :</span></p>
<p><span style="font-size:12.0pt; color:black"> 1/ the region extraction may need some resampling, so I need to be able to configure the resampling method</span></p>
<p><span style="font-size:12.0pt; color:black"> 2/ the extracted region boundaries do no necessary fit on exact pixels of the original dataset</span></p>
<p><span style="font-size:12.0pt; color:black"> 3/ the SRS will not be modified, but I may need a vertical datum shift (EGM96 to WGS84 for example)</span></p>
<p><span style="font-size:12.0pt; color:black"> 4/ the extraction will be repeated a lot (a lot !) to extract several "tiles" with different bounds : the application can work on really big rasters, so I prefer to avoid complex objects initialization for each
extraction</span></p>
<p><span style="font-size:12.0pt; color:black"> </span></p>
<p><span style="font-size:12.0pt; color:black">Should I :</span></p>
<p><span style="font-size:12.0pt; color:black"> </span></p>
<p><span style="font-size:12.0pt; color:black">- create a wrapped dataset (VRTDataSet) and make RasterIO on it ? This seems to solve 1/ and 3/ and 4/, but what about 2/ ?</span></p>
<p><span style="font-size:12.0pt; color:black"> </span></p>
<p><span style="font-size:12.0pt; color:black">- use a WarpOperation and then execute WarpRegionToBuffer method ? <span style="background:white">This seems to solve 1/ and 2/ and 3/, but what about 4/ ?</span></span></p>
<p><span style="font-size:12.0pt; color:black"> </span></p>
<p><span style="font-size:12.0pt; color:black; background:white">Any help will be appreciated.</span><span style="font-size:12.0pt; color:black"></span></p>
<p><span style="font-size:12.0pt; color:black"> </span></p>
<p><span style="font-size:12.0pt; color:black"> </span></p>
<p><span style="font-size:12.0pt; color:black; background:white">Thanks</span><span style="font-size:12.0pt; color:black"></span></p>
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