[mapserver-users] KKJ images misaligned after update

[Even Rouault]

On lundi 18 mai 2020 13:16:32 CEST Rahkonen Jukka (MML) wrote:
> Hi,
> 
> I got a report about a service that has been running fine for years but got
> broken now after following updates:
> 
> sqlite 3.29 -> 3.31
> proj 6.2.0 -> 6.3.0
> geos 3.7.2 -> 3.8.0
> gdal 2.4.2 -> 3.0.4
> mapserver 7.4.2 -> 7.4.3

I didn't try, but I'd strongly suspect the combination MapServer 7.4 + GDAL 3 doesn't work so 
well here. The issue you hit should be hopefully fixed with the following added code path in 
MapServer 7.6:
https://github.com/mapserver/mapserver/blob/
13607c79d8254326c83b1b8b2f81d2560169106c/mapogr.cpp#L959

Basically on reading the SRS from the TIFF file with GDAL, we used to export the WKT 
definition to a PROJ.4 string, and then built the Mapserver CRS object from it. Before GDAL 
3.X, this export to PROJ.4 string included TOWGS84 parameters. Since GDAL 3.X, it no longer 
does.

Hence the new code path, that detects that the CRS read from GDAL has an EPSG code 
attached, and when that's the case, instanciate a +init=epsg:XXXX string as the Mapserver 
CRS object to avoid going to potentially lossy PROJ.4 strings.

So "good" version combinations are probably:
- Mapserver 7.4 (or 7.6) + GDAL 2.4 + PROJ 5
- or MapServer 7.6 + GDAL 3.X + PROJ >= 6

Even

-- 
Spatialys - Geospatial professional services
http://www.spatialys.com
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