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

[Patrick Dunford]

Hello,

the issue is not with the performance drawing the raster, it is with the 
system only being able to have a certain number of file based rasters 
loaded in a project before it will crash.

On 22/11/19 11:08 AM, Alexandre Neto wrote:
> 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 <mailto: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 <http://www.qcooperative.net>
>>
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