[Qgis-user] QGIS: Reduction of resolution via pyramids only for defined scale range

[Jukka Rahkonen]

Julian Schall <j.schall at ...> writes:

> 
> 
> Hello members of the mailing list, 
>  
> I would appreciate help on the following problem: 
> I would like to improve the performance of a raster layer. Of course I can
build pyramids for that purpose. But in the scale ranges from 1:1 to
1:25.000 I need maximum resolution and detail. In this scale range, the
performance is sufficient even without pyramids. 
> Ideal would be that the pyramids respectively the reduction of the
resolution with improvement of performance is only applied to scales smaller
than 1:25,000. Is this possible in QGIS? 
>  
> Thanks for helpful answers! 
>  
> Kind regards 
>  
> Julian Schall

There are check boxes for overview levels in the Build overviews panel.
Level 2 means double the original pizel size etc. Leave for example levels 2
and 4 unchecked. However, level 2 means 25% extra disk space but level 4
only 6.25%. Thus it may not make sense to skip other levels than 2. Remember
to compress also the overviews and test with external overviews which you
can easily delete and continue with new tests. Internal overviews can be
removed so that they are no more used but operation does not make image
files smaller.