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

[Julian Schall]

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 < <mailto:jukka.rahkonen at mmmtike.fi>
jukka.rahkonen at mmmtike.fi>

To:  <mailto:qgis-user at lists.osgeo.org> qgis-user at lists.osgeo.org

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

      only for    defined scale range

Message-ID: < <mailto:loom.20140612T112229-91 at post.gmane.org>
loom.20140612T112229-91 at post.gmane.org>

Content-Type: text/plain; charset=utf-8

 

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