[QGIS-Developer] [Qgis-user] Handling a large number of raster layers with Qgis architectural limitations

[Alexandre Neto]

AFAIK,

WMST creates pyramids in cache as needed, hence it may do a better balance
between disk usage and performance. You can control the number of pyramid
layers you create and the compression format of it to save some space. But
having raster files with 4000x4000 pixels with no pyramids will make a full
read of the raster file to show even only a bit of it... That will make
QGIS performance really poor.

Thereºs this blog post from 2010 that does some comparison between several
formats and their sizes and performances. It's in portuguese, but I think
you can find ways of translating it.


https://blog.viasig.com/2010/01/mosaicos-de-imagens-em-mapserver-com-gdal/

Hope it helps

Alexandre Neto

On Thu, Nov 21, 2019 at 2:05 PM Patrick Dunford <enzedrailmaps at gmail.com>
wrote:

> Building pyramids gobbles up heaps of disk space. I tried pyramids on 157
> MB layer, which created an extra file 1.6 GiB.
>
> I can't see the WMTS building lots of temporary file pyramids using up disk
> On 18/11/19 10:50 PM, Alexandre Neto wrote:
>
> Hi Patrick,
>
> Sorry for asking, did you create pyramids (overlays) for your raster
> "tiles"?
>
> See more information about pyramids on QGIS official documentation:
>
>
> https://docs.qgis.org/3.4/en/docs/user_manual/working_with_raster/raster_properties.html#pyramids-properties
>
> To create pyramids on many files, it's probably better to use GDAL
> directly to process all files in a folder:
>
> https://gdal.org/programs/gdaladdo.html
>
> My feeling is that the WMS service is doing that for you, and that's the
> reason why it works well with a service.
>
> Alexandre Neto
> QGIS Support
> www.qcooperative.net
>
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