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

[Jonathan Moules]

Hi Julian,
  You can specify at what levels pyramids are created. That's what the
"resolutions" box on the right does. The problem is, knowing which levels
you want.

So if your data is a 4000x4000 tiff then it'll offer to create pyramids at:

> 2000*2000
> 1000*1000
> 500*500
> 250*250
> 125*125
> 63*63


I'm going to guess at the answer to your question - I believe what you need
to do is the following:

- Find out what the scale is for "Zoom to best scale (100%)" for the
raster. For my raster it's 1:9,449 (yours will be obviously be different).
- So the 2000x2000 pyramid will have a scale of 1:18898 (i.e. double 9449).
So you wouldn't want that level. In this scenario you may want 1000*1000 -
which would be for a scale of 1: 37796 (double 1:18898).

So with some simple maths you can figure out which pyramid levels you want.
I suppose it would be a good feature for QGIS to show scales rather than
tile sizes in the "resolutions" box. I'll go open a feature suggestion for
that one.

Cheers,
Jonathan


On 12 June 2014 10:00, Julian Schall <j.schall at ff-forst.de> wrote:

> 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
>
>
>
> _______________________________________________
> Qgis-user mailing list
> Qgis-user at lists.osgeo.org
> http://lists.osgeo.org/mailman/listinfo/qgis-user
>

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