[gdal-dev] Gdalinfo slow with big Rasterlite tables

[Jukka Rahkonen]

Hi,

I converted 153600 x 249600 pixels of rasterdata into a
Rasterlite table. After creating overviews the result
behaves well in Quantum GIS once the table is opened.
Unfortunatly opening the table with QGis installed on a
mini PC takes ages.

I do not know what QGis is really doing but I guessed that
perhaps it wants to know some metadata and makes a
gdalinfo request or something equivalent. Therefore I made
a test with bit more powerful computer and running
gdalinfo with that took about 3 minutes. That feels rather
slow.

Is gdalinfo perhaps walking through every single tile in the
rasterlite table for gathering the image layer info? Could
there be any other way to do it in more effective way on the
GDAL side?

I have a feeling that this may not be really a GDAL
problem. Doing plain SELECT count(*) from test_rasters
with Spatialite-gui is also very slow and took about the
same 3 minutes in my rapid test. That makes me think that
for getting more speed Rasterlite should store more info
about tiles into raster_metadata tables for providing an
instant access to data. Perhaps this is something to talk
with Alessandro who is developing a new Rasterlite 2 which
should be ready by the end of this year.

When it comes to GDAL, could it make any sense to cache
gdalinfo from Rasterlite layers? Three minutes is rather a
long time and my 153600 x 249600 pixel sized layer with
780270 rows/tiles in 5 meter resolution in the table is
not exceptionally big. If time is increasing with tile
count it would mean 12 minutes for getting gdalinfo from
2.5 meter resolution and 48 minutes from 1.25 minutes
layer...

Test with gdal_translate makes me feel that it is also
reading the layer info first and spending about 3 minutes for
that before starting the real work. Timing is very uncertain
though, I could only take the time before the progress bar
appears on the screen.

-Jukka Rahkonen-