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

[Nicolas Cadieux]

Hi Patrick,
How many files are we dealing with before it crashes? 
Nicolas

> Le 27 nov. 2019 à 22:35, Patrick Dunford <enzedrailmaps at gmail.com> a écrit :
> 
> 
> 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> 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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