Hi,
On 07/25/2018 06:00 PM, Even Rouault wrote:
Is this supported behavior, should I be able to read these files remotely,
and do windowed reads on them?
For windowed reads, you need to prefix with /vsicurl/, but I don't guarantee
the efficiency of this with JPEG2000 in general, and with JP2OpenJPEG in
particular.
Regarding "efficiency" I'd like to add two observations from a little
investigation (not really in-depth) I did recently to compare /vsicurl/
with a tiny, experimental JS lib (fetch & decode single jp2 tiles in
pure JS):
- If I try to fetch a window that is completely within one tile it
*seems* vsicurl is iterating through all tiles and does not stop after
reaching & fetching the "requested" tile.
- Instead of starting from the first tile it could make a guess and
start at that offset and search backwards and forward till it finds the
requested tile index. Although a good "guess" of an offset is difficult
given that tile size might vary greatly.
I think this could probably make fetching parts slightly more efficient
(in terms of no. of requests & data transfer). Certainly it would be
much easier if tile offsets could be included in a jp2 header.
Jan
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