[gdal-dev] GeoTIFF in South Africa

[Javier Jimenez Shaw]

Hi

I got a GeoTIFF from South Africa that is displayed in the Mediterranean
sea in QGIS.

$ gdalinfo sa.tif
Driver: GTiff/GeoTIFF
Files: sa.tif
Size is 1305, 909
Coordinate System is:
PROJCRS["Hartebeesthoek94 / Lo21",
    BASEGEOGCRS["Hartebeesthoek94",
...
    ID["EPSG",2049]]
Data axis to CRS axis mapping: 1,2
Origin = (-43632.855010000006587,-3629566.022050000261515)
Pixel Size = (0.275826758620690,-0.275760660066007)
Metadata:
  AREA_OR_POINT=Area
  TIFFTAG_SOFTWARE=pix4dmapper
Image Structure Metadata:
  COMPRESSION=LZW
  INTERLEAVE=PIXEL
  PREDICTOR=2

As you can see, the Origin is very negative, and in Lo21 it should be
positive.
Ok, lets change the geotransform parameters:

$ gdal_translate -a_gt 43632.8550100000 -0.275760660 0 3629566.0220500 0
0.27576066 -co COMPRESS=LZW -co PREDICTOR=2 sa.tif sa.located.tif
$ gdalinfo sa.located.tif
Driver: GTiff/GeoTIFF
Files: sa.located.tif
Size is 1305, 909
Coordinate System is:
PROJCRS["Hartebeesthoek94 / Lo21",
    BASEGEOGCRS["Hartebeesthoek94",
        DATUM["Hartebeesthoek94",
...
    ID["EPSG",2049]]
Data axis to CRS axis mapping: 1,2
Origin = (43632.855009999999311,3629566.022049999795854)
Pixel Size = (-0.275760660000000,0.275760660000000)

That appears properly located in QGIS. But I think that due to the signs in
the pixel size, it is performing really bad (it is not doing some
optimizations)

I run gdalwarp hoping that it changes it. And it does in GDAL 3.8.4
$ gdalinfo --version
GDAL 3.8.4, released 2024/02/08
$ gdalwarp sa.located.tif sa.cog.3.8.4.tif -of COG
$ gdalinfo sa.cog.3.8.4.tif
Driver: GTiff/GeoTIFF
Files: sa.cog.3.8.4.tif
Size is 1305, 909
Coordinate System is:
PROJCRS["Hartebeesthoek94 / Lo21",
    BASEGEOGCRS["Hartebeesthoek94",
    ID["EPSG",2049]]
Data axis to CRS axis mapping: 1,2
Origin = (43272.987348700000439,3629816.688489940017462)
Pixel Size = (0.275760660000079,-0.275760660000079)

See how it changes the origin and the signs of the pixel size

However in 3.11.4 it is different

$ gdalinfo sa.cog.3.11.4.tif
Driver: GTiff/GeoTIFF
Files: sa.cog.3.11.4.tif
Size is 1305, 909
Coordinate System is:
PROJCRS["Hartebeesthoek94 / Lo21",
    BASEGEOGCRS["Hartebeesthoek94",
...
    ID["EPSG",2049]]
Data axis to CRS axis mapping: 1,2
Origin = (43632.855009999999311,3629816.688489940017462)
Pixel Size = (-0.275760660000000,-0.275760660000000)

Having the negative pixel size for the first coordinate is affecting the
performance in QGIS?

Is there a better way to do all this?

Thank you,
Javier
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