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Hi Jukka,<br>
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I'm off work now so can't check the image type until next week, but the extents<span id="ms-outlook-android-cursor"></span> are the same at both GDAL 2 and GDAL 3. At v3, there is a repeated column of pixels at the right hand edge. I guess there is no more
data, so it is padded to fill the required extent.<br>
<br>
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Jon<br>
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<div id="divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" style="font-size:11pt" color="#000000"><b>From:</b> gdal-dev <gdal-dev-bounces@lists.osgeo.org> on behalf of jratike80 <jukka.rahkonen@maanmittauslaitos.fi><br>
<b>Sent:</b> Tuesday, December 22, 2020 7:47:04 PM<br>
<b>To:</b> gdal-dev@lists.osgeo.org <gdal-dev@lists.osgeo.org><br>
<b>Subject:</b> Re: [gdal-dev] Duplicate pixels in VRT</font>
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<div class="PlainText">Hi,<br>
<br>
Check what are the extents of two adjacert images reported by GDAL 2 and 3,<br>
as well as the sizes in pixels, and if images are of type "pixel is area" or<br>
"pixel is point". DEM kind of images are sometimes intentionally produced to<br>
have overlap.<br>
<br>
-Jukka Rahkonen-<br>
<br>
<br>
<br>
Jon Morris wrote<br>
> Hello all,<br>
> <br>
> I've come across a weird edge case and I'm wondering if anyone has seen<br>
> something similar.<br>
> <br>
> I'm updating our application from GDAL v2.2 to v3.2 and have a failing<br>
> test where there is a 1 pixel shift in the output. We're building a VRT<br>
> from a DTM and a flood depth raster and when you call ds.ReadAsArray() on<br>
> the VRT there is a duplicated column of pixels at GDAL 2, which is causing<br>
> the apparent shift. It's not worth raising a ticket, as the GDAL 3 output<br>
> is correct, but I can't explain why this shift has happened and I'm<br>
> wondering if this has happened anywhere else.<br>
> <br>
> If I open the two VRTs in QGIS, they look the same, so maybe it's an issue<br>
> with ReadAsArray. There is slight difference in SRS precision, which might<br>
> be causing a rounding error, but otherwise I've no idea what might be<br>
> causing it.<br>
> <br>
> GDAL 2<br>
> <SRS><br>
> PROJCS["North_America_Albers_Equal_Area_Conic",<br>
> GEOGCS["NAD83",DATUM["North_American_Datum_1983",<br>
> SPHEROID["GRS<br>
> 1980",6378137,298.2572221010042,AUTHORITY["EPSG","7019"]],AUTHORITY["EPSG","6269"]],<br>
> PRIMEM["Greenwich",0],UNIT["degree",0.0174532925199433],AUTHORITY["EPSG","4269"]],<br>
> PROJECTION["Albers_Conic_Equal_Area"],<br>
> PARAMETER["standard_parallel_1",20],<br>
> PARAMETER["standard_parallel_2",60],<br>
> PARAMETER["latitude_of_center",40],<br>
> PARAMETER["longitude_of_center",-96],<br>
> PARAMETER["false_easting",0],<br>
> PARAMETER["false_northing",0],UNIT["metre",1,AUTHORITY["EPSG","9001"]]]<br>
> </SRS><br>
> GDAL 3<br>
> <SRS dataAxisToSRSAxisMapping="1,2"><br>
> PROJCS["North_America_Albers_Equal_Area_Conic",<br>
> GEOGCS["NAD83",DATUM["North_American_Datum_1983",<br>
> SPHEROID["GRS<br>
> 1980",6378137,298.257222101004,AUTHORITY["EPSG","7019"]],AUTHORITY["EPSG","6269"]],<br>
> PRIMEM["Greenwich",0],UNIT["degree",0.0174532925199433,AUTHORITY["EPSG","9122"]],AUTHORITY["EPSG","4269"]],<br>
> PROJECTION["Albers_Conic_Equal_Area"],<br>
> PARAMETER["latitude_of_center",40],<br>
> PARAMETER["longitude_of_center",-96],<br>
> PARAMETER["standard_parallel_1",20],<br>
> PARAMETER["standard_parallel_2",60],<br>
> PARAMETER["false_easting",0],<br>
> PARAMETER["false_northing",0],UNIT["metre",1,AUTHORITY["EPSG","9001"]],AXIS["Easting",EAST],AXIS["Northing",NORTH]]<br>
> </SRS><br>
> Thanks,<br>
> <br>
> Jon<br>
> <br>
> <br>
> Jon Morris<br>
> Software Developer<br>
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