[MapProxy] Printing issues since QGIS 3.40 with integration of Mapproxy WMS service

[Daniel Cebulla]

Hello list,

is there anyone here who uses QGIS / QGIS Server besides mapproxy and 
use mapproxy layers within QGIS / QGIS Server for printing?

I have a very strange problem.

In certain cases, QGIS does not generate a complete map image as print 
output, if a mapproxy layer is integrated as a WMS layer. In such a 
case, only one tile row of the map is appearing in the map printout and 
the rest is empty.
For instance, this looks like this in A3 with 1 : 10,000: 
https://cloud.jena.de/index.php/s/jS7CpIpPVxSzBh7

The whole thing can be reproduced in QGIS Desktop, but the problem also 
occurs with a direct GetPrint request (in my case via the QGIS Web 
Client). Interestingly, this only happens from QGIS 3.40 onwards, in the 
versions before (with 3.34 lts but also tested with 3.38) it works. It 
also works with 96 dpi print resolution (or I have not found a scale 
yet, where the problem also occurs) but not with 300 dpi.

At first I suspected that this was somehow related to the cache 
resolutions configured in Mapproxy. However, the problem also occurs if 
I configure the WMS services directly as "sources" in the print layer in 
Mapproxy and do not use a cache with corresponding grids at all, but 
only pass the WMS services through. Where do the tiles come from if 
there is no grid?

I could not reproduce the problem with the integration of other external 
mapping services, I had found this online 
https://www.orka-mv.de/geodienste/orkamv/service. So it should somehow 
(also) be due to the Mapproxy configuration, but why does the problem 
only occur with QGIS 3.40 and before that it worked? I haven't found any 
issues/commits in the QGIS Github repo where I could find out where the 
problem comes from.

It's all very mysterious and I'm pretty clueless.

So if anyone has a similar setup and can reproduce the problem or has a 
tip as to what the problem could be or what has changed in QGIS with 
3.40, I would be grateful for anything!

Best regards
Daniel

-- 
Daniel Cebulla
Application support GIS
on behalf of Dr. Arndt Döhler

Phone: +493641 49-5190      Mail: daniel.cebulla at jena.de

Kommunale Informationstechnik und Telekommunikation (KITT)

Municipal enterprise        Director of Operations: Dr. Arndt Döhler
of the city of Jena         Paradiesstr. 6, 07743 Jena