[postgis-devel] [raster] Tweaking overviews in raster2pgsql.py

[Pierre Racine]

+1

>-----Original Message-----
>From: postgis-devel-bounces at postgis.refractions.net [mailto:postgis-devel-
>bounces at postgis.refractions.net] On Behalf Of Mateusz Loskot
>Sent: 2 décembre 2010 13:06
>To: postgis-devel at postgis.refractions.net
>Subject: [postgis-devel] [raster] Tweaking overviews in raster2pgsql.py
>
>Hi,
>
>I'd like to propose a small simplification to the overviews management
>in the raster loader script. Currently, raster2pgsql.py takes explicit
>overview factor (called level, incorrectly in my opinion).
>This follows gdaladdo appraoch where it accepts list of overview
>reduction factors used to generate overview levels.
>
>I'd like to get rid of this explicit factors and simplify things a bit,
>I'd like to follow the techniques users already know from slippy maps,
>Google Maps, Oracle etc.
>
>The command would change from
>
>raster2pgsql.py -t mydata  ... (base level)
>raster2pgsql.py -t mydata -l 2 ...
>raster2pgsql.py -t mydata -l 4 ...
>raster2pgsql.py -t mydata -l 8 ...
>...
>
>The command would change to simple:
>
>raster2pgsql.py -t mydata -l 8 ...
>
>where the N=8 means that user requests 8 overview levels in total,
>including base raster.
>The levels are numbered as follows: 0, 1, 2, ..., N-1
>The overview reduction factor is calculated based on level number:
>
>2 ^ Ni
>
>where Ni is the actual level number:
>
>level=0 => overview factor=1 (base raster)
>level=1 => overview factor=2 (reduction by 2)
>level=2 => overview factor=4 (reduction by 4)
>... etc.
>
>This would generate overview tables named after overview level
>but not overview factor. The latter is already stored in metadata.
>
>mydata (base raster)
>mydata_o_1 (overview factor=2)
>mydata_o_2 (overview factor=4)
>mydata_o_3 (overview factor=8)
>...
>
>This calculation is reversible making it possible to calculate overview
>level from given reduction factor:
>
>level = log(overview_factor) / log(2)
>factor = pow(2, level)
>
>The simplification is that there is only *one* variable information
>carried around, it is total number of overview levels.
>All the rest values are easily calculated based on that.
>
>
>What you say?
>
>Best regards,
>--
>Mateusz Loskot, http://mateusz.loskot.net
>Charter Member of OSGeo, http://osgeo.org
>Member of ACCU, http://accu.org
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