[gdal-dev] Questions about SQL cursors in GDAL driver

[Frank Warmerdam]

Jorge Arévalo wrote:
> So, clearly, I have a mistake. Think in a table with tiles of 100x100
> px. We have 30 tiles. When I create RasterBands, their block size will
> be 100x100. So, IReadBlock(0, 0, bufffer) indicates the block going
> from (0, 0) to (100, 100). Does it mean that the block from (0, 0) to
> (100, 100) must be the first one in the table if I get the rows
> ordered by rid? 

No, I do not see how you could depend on this.

> It depends on how the tiles have been loaded. So,
> instead of making hypothesis, Should I query the block that matchs the
> extent from (0, 0) to (100, 100)?

Yes, but furthermore, you will need to transform the pixel bounds into
georeferenced coordinates to do the spatial query.  I would also note that
you might be best to reduce the query rectangle to just be a small central
area of the tile to avoid fetching adjacent tiles or even forcing
postgres to fetch them to check their bounds against your point.  Spatial
index tend to have a certain granularity.

Best regards,
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