[gdal-dev] Idea: support JP2 TLM as sidecar in GDAL/OpenJPEG

[Jérémy Anger]

Dear GDAL maintainers,

Thank you for the release of OpenJPEG 2.5.3, with the support of TLM
markers!
Following up on [1], Sentinel-2 JP2 files currently do not have TLM
markers. However, it is theoretically possible to generate an external
index file for each JP2 raster, and the index could be formatted exactly as
a JP2 TLM marker. Such sidecar file is not part of the JPEG2000 standard,
but given the gains that are achievable with TLM markers, this strategy
sounds reasonable. The entirety of the Sentinel-2 collection (archive and
live) is concerned.

GDAL could be modified to look for these sidecar .tlm files (although I'm
not too familiar with the sidecar system), and give the TLM marker content
to JP2 implementations (OpenJPEG in particular, after changes).

Do you think this approach is reasonable? Would it be reasonable to
implement such a feature in GDAL and OpenJPEG?
Do you have ideas for a better solution?

Best regards,
Jérémy

[1]: https://lists.osgeo.org/pipermail/gdal-dev/2024-November/059805.html
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