[Qgis-user] Data volume wms-layer

[Patrick Dunford]

I left this question for a few days because I hoped someone with more 
technical knowledge than me of how Qgis works with this type of data 
would be able to answer your question. As a user I don't have the same 
technical insight as one of the developers who may be reading this 
question and more familiar with data processing in the software.

I currently work with projects that use large numbers of data layers of 
raster type, however in my case they are all in files that I have 
downloaded to my computer and loading locally, rather than any type of 
data that could be accessed from an online server.

I have found in experience with working with raster layers that Qgis 3 
is handling them quite differently from previous versions (I have been 
using Qgis since 1.8). It was not until version 2.14 that I started 
working with the projects using these large numbers of raster images, 
and have been using them through 2.14, 2.16 and 2.18 and now in releases 
of version 3.

The map projects I am working on cover a part of New Zealand 
specifically a corridor around 6000 kilometres long and about 20 metres 
wide which is covered by geojpeg rasters varying from 0.4 to 0.1 metre 
per pixel resolution and the size of each raster is generally 4800x7200 
pixels.

The experience I had is that Qgis 3.x appears to be caching a lot more 
raster data in memory than I saw with 2.x and it seems to be caching 
every raster in my project, not just the ones that I am displaying at 
the moment. It uses up the resources in my system a lot faster than 2.x 
ever did. And if I use larger size raster files, I have seen it run out 
of resources on the system more than once.

So in terms of the way it consumes resources for rasters, my experience 
is more related to the way I see it using up the physical resources on 
my computer like the physical or virtual memory. I ended up adding more 
RAM to my system and more swap disk space to help deal with the extra 
drain on resources that has happened since upgrading to version 3.

There is a section in the settings dialog that specifically relates to 
rendering. I'm not completely confident this is the type of situation 
that would be relevant to your scenario. It may affect my situation more 
if I spent some time playing with these settings (render caching for 
example) but it might not be so relevant to you, unless the render 
caching is causing the software to download a lot of raster data from 
your WMS server. You could try experimenting with some of those settings.

On 20/03/19 2:08 AM, Pascale Hutter wrote:
> Hi Patrick
>
> Thanks for your interest! Its raster data of aerial images 
> (https://shop.swisstopo.admin.ch/de/products/geoservice/swisstopo_geoservices/swisstopoWMS). 
> I often use this for small environmental projects of mine, where I 
> have no budget to buy any additional data. So far the 5’000 Megapixel 
> were enough to work during the whole year. Now it was finished up 
> within a month, although I did much less work.
> I did read, that the whole wms-layer part was newly written for the 
> QGIS version 3.x, so maybe this has something to do with it?
>
> Thank you for any kind of help!
>
> Pascale
>
> M. Sc. Biologie
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>> Am 19.03.2019 um 13:33 schrieb Patrick Dunford 
>> <enzedrailmaps at gmail.com <mailto:enzedrailmaps at gmail.com>>:
>>
>> What is the type of data which is within your wms layer. Is this 
>> vector or raster type of data?
>>
>> On 19/03/19 12:59 AM, Pascale Hutter wrote:
>>> Hi there,
>>>
>>> I’m quite new to QGIS version 3, and was before working with QGIS 
>>> 2.18. I often use wms-layer, where I purchase a certain data-volume 
>>> (p. ex. 5’000 pixel) to work with. However, with the new QGIS 3.0 
>>> this data volume is used up far more quickly. In QGIS 2.18 it lasted 
>>> a lot longer. I was wondering if any of you mades some similar 
>>> experiences? Do you have any idea, if there is a way to change the 
>>> settings so the data volume would last longer again?
>>>
>>> Thank you very much for any suggestions!
>>>
>>> Pascale
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
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