[gdal-dev] Duplicate pixels in VRT

Wed Dec 23 00:52:25 PST 2020

Hi Jukka,

I'm off work now so can't check the image type until next week, but the extents 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.

Jon

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________________________________
From: gdal-dev <gdal-dev-bounces at lists.osgeo.org> on behalf of jratike80 <jukka.rahkonen at maanmittauslaitos.fi>
Sent: Tuesday, December 22, 2020 7:47:04 PM
To: gdal-dev at lists.osgeo.org <gdal-dev at lists.osgeo.org>
Subject: Re: [gdal-dev] Duplicate pixels in VRT

Hi,

Check what are the extents of two adjacert images reported by GDAL 2 and 3,
as well as the sizes in pixels, and if images are of type "pixel is area" or
"pixel is point". DEM kind of images are sometimes intentionally produced to
have overlap.

-Jukka Rahkonen-

Jon Morris wrote
> Hello all,
>
> I've come across a weird edge case and I'm wondering if anyone has seen
> something similar.
>
> I'm updating our application from GDAL v2.2 to v3.2 and have a failing
> test where there is a 1 pixel shift in the output. We're building a VRT
> from a DTM and a flood depth raster and when you call ds.ReadAsArray() on
> the VRT there is a duplicated column of pixels at GDAL 2, which is causing
> the apparent shift. It's not worth raising a ticket, as the GDAL 3 output
> is correct, but I can't explain why this shift has happened and I'm
> wondering if this has happened anywhere else.
>
> If I open the two VRTs in QGIS, they look the same, so maybe it's an issue
> with ReadAsArray. There is slight difference in SRS precision, which might
> be causing a rounding error, but otherwise I've no idea what might be
> causing it.
>
> GDAL 2
> <SRS>
> PROJCS["North_America_Albers_Equal_Area_Conic",
> GEOGCS["NAD83",DATUM["North_American_Datum_1983",
> SPHEROID["GRS
> 1980",6378137,298.2572221010042,AUTHORITY["EPSG","7019"]],AUTHORITY["EPSG","6269"]],
> PRIMEM["Greenwich",0],UNIT["degree",0.0174532925199433],AUTHORITY["EPSG","4269"]],
> PROJECTION["Albers_Conic_Equal_Area"],
> PARAMETER["standard_parallel_1",20],
> PARAMETER["standard_parallel_2",60],
> PARAMETER["latitude_of_center",40],
> PARAMETER["longitude_of_center",-96],
> PARAMETER["false_easting",0],
> PARAMETER["false_northing",0],UNIT["metre",1,AUTHORITY["EPSG","9001"]]]
> </SRS>
> GDAL 3
> <SRS dataAxisToSRSAxisMapping="1,2">
> PROJCS["North_America_Albers_Equal_Area_Conic",
> GEOGCS["NAD83",DATUM["North_American_Datum_1983",
> SPHEROID["GRS
> 1980",6378137,298.257222101004,AUTHORITY["EPSG","7019"]],AUTHORITY["EPSG","6269"]],
> PRIMEM["Greenwich",0],UNIT["degree",0.0174532925199433,AUTHORITY["EPSG","9122"]],AUTHORITY["EPSG","4269"]],
> PROJECTION["Albers_Conic_Equal_Area"],
> PARAMETER["latitude_of_center",40],
> PARAMETER["longitude_of_center",-96],
> PARAMETER["standard_parallel_1",20],
> PARAMETER["standard_parallel_2",60],
> PARAMETER["false_easting",0],
> PARAMETER["false_northing",0],UNIT["metre",1,AUTHORITY["EPSG","9001"]],AXIS["Easting",EAST],AXIS["Northing",NORTH]]
> </SRS>
> Thanks,
>
> Jon
>
>
> Jon Morris
> Software Developer
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