Hi,
here's a related thread (i.e. xyz tiles, but I guess it's also valid vor
wms):
https://github.com/qgis/QGIS/issues/34813
Some quotes:
"QGIS renders the surrounding areas in a background job to make
subsequent pan actions faster. Therefore it sends more tile requests
than necessary for the current map extent."
"Btw, we now have the code in place to fine-tune prefetching behavior
for all raster layers on a per-layer basis, for now I just blacklisted
osm tiles."
It sounds like the plan is to make the prefetching behavior configurable
via QGIS settings.
Cheers,
Bjoern
On 13.02.2021 19:45, Jeff McKenna wrote:
Hi Richard,
Yes I've noticed this also, I just never spent time to examine why.
For example, using my own WMS service I zoomed in and QGIS fired 11
GetMap requests to my server. It's difficult to trigger though (I
can't reproduce with your NL service). Bizarre. But I have
definitely seen 9+ GetMap requests for the same service/layer.
-jeff
--
Jeff McKenna
GatewayGeo: MapServer Consulting and Training Services
co-founder of FOSS4G
http://gatewaygeo.com/
On 2021-02-13 11:29 a.m., Richard Duivenvoorde wrote:
Hi,
As a vivid WMS user/debugger, I see that QGIS is firing 9 requests per
'view-extent' currently.
I'm aware of cache etc etc... but... especially when using temporal
filters for example, do others agree with me that this is more or less
useless?
I'm also aware that a lot of WMS are actually just WMS interfaces in
front of a cached WMTS, but still.
- some (governmental) services nowadays are still free for fair use,
but: firing 9 times the actual requests costs resources/energy/maybe
money
- before the WMTS I ran WMS services sometimes with pretty heavy
styling, so on higher zoomlevels you do NOT want your clients to fire
9 requests, and just effectively use 1 ...
So in short: should I try to add some kind of (hidden?) option to
minimize the number of requests?
To test a wms of all municipalities of NL:
https://geodata.nationaalgeoregister.nl/bestuurlijkegrenzen/ows?SERVICE=WMS
(layer 'gemeenten', EPSG:28992)
And look in F12/debugging window the number of GetMap requests fired
when zoomed in...
I copied/created polgyons of the requests, and (see screenie) indeed
looking at the center 'tile', the 8 surrounding requests are also
fired....
Currently looking into this.
Regards,
Richard Duivenvoorde
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