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Using QGIS 3.28.11, I have a very big file (0,5 Gb) which is oriented but not to scale (definition unknown) and not georeferenced (but the coordinate system used when creating the file is known).

Is there a way to create a spatial reference file to be then applied to the already existing file, without creating a new output georeferenced TIFF file which my computer would hardly be able first to generate, then to read?

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    The word "big" when referring to a TIFF is expected to be in excess of 4GiB, a BigTIFF (which uses 64-bit addressing). 500 MiB isn't particularly large in the spectrum of TIFF file sizes (only 12.5% of capacity), though this is the compressed size so the actual rows x cols x bands x bits / 8 data size could be larger. Georeferencing will generally result in rotation, which would result in a raster up to four times as large. There are processing techniques which can improve image render performance, but this adds another 33%. You need to choose between size and performance.
    – Vince
    Oct 2, 2023 at 12:16

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One alternative is to use gdal_edit https://gdal.org/programs/gdal_edit.html that can update the metadata of the image file without re-writing the pixels. The utility has three options, consider if they serve well enough for your use case

-a_srs <srs_def>

Defines the target coordinate system. This coordinate system will be written to the dataset. If the empty string or None is specified, then the existing coordinate system will be removed (for TIFF/GeoTIFF, might not be well supported besides that).

-a_ullr

Assign/override the georeferenced bounds of the dataset.

-a_ulurll

Assign/override the georeferenced bounds of the dataset from three points: upper-left, upper-right and lower-left. Unlike -a_ullr, this also supports rotated datasets (edges not parallel to coordinate system axes).

New in version 3.1.

Gdal_edit is a Python script and you must have GDAL Python bindings installed for using it.

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... The answer was here: "The Linear algorithm is used to create a world file and is different from the other algorithms, as it does not actually transform the raster pixels. It allows positioning (translating) the image and uniform scaling, but no rotation or other transformations. It is the most suitable if your image is a good quality raster map, in a known CRS, but is just missing georeferencing information. At least 2 GCPs are needed. [...] " And there: "The Create world file checkbox is only available if you decide to use the linear transformation type, because this means that the raster image actually won’t be transformed. In this case, the Output raster field is not activated, because only a new world file will be created".

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  • My image file was a zipped jpeg. The output World file was a *.wld file. I changed it to a *.jpw file and zipped it with the image file.
    – Henème
    Oct 2, 2023 at 12:33
  • Despite what is said in the QGIS documentation, the Create World file was also available for the Helmert algorithm, which was far better and useful (georeferencing gave me a -0,35° rotation)
    – Henème
    Oct 2, 2023 at 12:35

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