[gdal-dev] Questions about SQL cursors in GDAL driver
Frank Warmerdam
warmerdam at pobox.com
Fri Jul 10 19:18:19 EDT 2009
Jorge Arévalo wrote:
> Hello,
>
> 2009/7/10 Tamas Szekeres <szekerest at gmail.com>:
>> Jorge,
>>
>> I'm a bit hesitant to think using a server cursor would be the best approach
>> here. Could you explain why is this needed?
>
> Yes. As now I'm working basically with regularly tiled coverages, an
> operation like SELECT rast FROM table gives me all the tiles. These
> tiles don't overlap, and its size can be the size of a block read for
> IReadBlock method. So, if I have a cursor, I can fetch the tile that
> the IRasterBlock needs as one of the rows of the resultset without
> having all the tiles loaded in memory at same time.
Jorge,
I'm not clear on how you know what row to take out of the resultset
for a given IReadBlock() call? How do you translate the x/y block
index into a resultset row offset?
I would note that spatial searches *should* be quite fast if the
raster row is spatially indexed.
Best regards,
--
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I set the clouds in motion - turn up | Frank Warmerdam, warmerdam at pobox.com
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