Hi,

I am currently using GDAL 3.1.3 and Mapserver 7.6.2 on a Ubuntu machine. I 
created a layer using a GRIB2 file as the source data.

When I tested the layer on QGIS 3.20, I noticed that it does not output 
correctly. When I'm zooming or moving the viewing extent to visualize the layer 
or data, the style constantly changes. I tested with WMS GetMap requests 
through a browser and the output issue is still there. See example GIF here: 
https://pasteboard.co/wAmyAUDyEeZs.gif

I validated the different classes (CLASS) in the style used in the mapfile and 
everything seems to be in order. From what I understand, Mapserver seems to do 
some interpolation, but I can't quite understand how it affects the output on 
that scale. I investigated and checked if the source file was the issue, but 
from what I see it doesn't seem like it's the case, as I tested with other data 
from another source file in NetCDF, and the issue is still there.

I created a test case to show you the issue here:


·       Sample mapfile: https://pastebin.com/KC3UkR4m


·       GRIB2 Source file (available here: 
https://dd.weather.gc.ca/model_hrdps/continental/grib2/00/001/) for the source 
data (using following patterns) : 
/CMC_hrdps_continental_PTYPE_SFC_0_ps2.5km_*.grib2/

Do you have an idea what could be the issue or how the interpolation works, and 
how to solve this issue?

Thanks a lot in advance for your answer(s)!

Félix Laframboise


Félix Laframboise, B.Sc.
Développeur géospatial / Geospatial developer
Systèmes de données géospatiales et ouvertes
Geospatial and Open Data Systems
Service Météorologique du Canada
Meteorological Service of Canada
Environnement et Changement Climatique Canada
Environment and Climate Change Canada
felix.laframbo...@ec.gc.ca<mailto:felix.laframbo...@ec.gc.ca>

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