[Qgis-user] QGIS: Reduction of resolution via pyramids

[Etienne Tourigny]

read on overviews in these 2 links

http://www.gdal.org/gdaladdo.html


http://www.gdal.org/frmt_gtiff.html


On Thu, Jun 12, 2014 at 10:46 AM, Julian Schall <j.schall at ff-forst.de>
wrote:

> Dear Jukka,
>
>
>
> thank you for your answer.
>
> I still don’t know how to build pyramids just for defined scale ranges (in
> my case: smaller then 1:25.000).
>
> I’ve forgotten to tell you an –maybe important- detail: I’m working with a
> virtual raster catalogue which i built out of 875 .jpgs (4000x4000).
>
> When building pyramids, i’ve always used the option “external (Erdas
> Image.aux)”.
>
> Can you shortly explain the difference between the 3 options (external
> .ovr, internal, external .aux)?
>
> I couldn’t find an advice in the handbook or via google.
>
> The QGIS instructions say that after building pyramids QGIS automaticly
> takes the best resolution when loading raster layers. So how can I
> influence what resolution QGIS chooses?
>
>
> Thanks again for further help!
>
> Kind regards,
>
>
> Julian Schall
>
>
>
>
>
> Date: Thu, 12 Jun 2014 09:34:18 +0000 (UTC)
>
> From: Jukka Rahkonen <jukka.rahkonen at mmmtike.fi>
>
> To: qgis-user at lists.osgeo.org
>
> Subject: Re: [Qgis-user] QGIS: Reduction of resolution via pyramids
>
>       only for    defined scale range
>
> Message-ID: <loom.20140612T112229-91 at post.gmane.org>
>
> Content-Type: text/plain; charset=utf-8
>
>
>
> 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.
>
>
>
>
>
>
>
>
>
>
>
> ------------------------------
>
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>
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