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

[Mateusz Loskot]

*bump*

On 02/12/10 18:06, Mateusz Loskot wrote:
> 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