[gdal-dev] Issue with GDAL - JP2KAK driver
even.rouault at spatialys.com
Sun Jun 28 07:11:37 PDT 2020
On dimanche 28 juin 2020 12:36:47 CEST Boris Forzun wrote:
> Thanks for the response,
> the image is indeed RPCL,
> doesn't that mean that the bits for the overview are not scattered through
> the file?
They are extra considerations:
- if your image is tiled, and the area you request covers several tiles, then the JPEG2000
codec may have to seek in different parts of the file for each tiles covered by your request
- it also depends on the strategy of the encoder to dispatch the tile-parts inside the file, in
case they are multiple tiles or tiles are encoded in several tile-parts (even for a tiled image, a
smart encoder might pack together tile-parts corresponding to lower resolution levels at the
beginning of the file)
- the presence of PLT marker segments might help a lot if the packets for lower resolutions
aren't in dedicated tile-parts.
I've just tried with a single-tiled RPCL image, with PLT marker segments, and when requesting
exactly at the resolution of the smallest overview, it only reads the beginning of the file.
Spatialys - Geospatial professional services
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