[mapserver-users] KKJ images misaligned after update

Mon May 18 06:16:32 PDT 2020

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

What breaks is an orthophoto layer that has source files in many CRSs. The source CRS may be EPSG:2391, 2392, 2393, 2395, and 3067, and the output is EPSG:3067. What happens is that the images in 239x series using the Finnish KKJ datum are not reprojected correctly. It seems that the affine transformation parameters (TOWGS84[-96.062,-82.428,-121.753,4.801,0.345,-1.376,1.496]) of the Finnish KKJ system http://epsg.io/2393 are not used.

I made a small test-zip into http://latuviitta.org/downloads/kkjtest.zip. It works fine for me with MS4W (Mapserver 7.6.0dev, GDAL 2.4.4, Proj 5.2.0) but with the updated system the middle tile takes quite an offset  (kkj_wrong.jpeg). The middle image is in EPSG:2393, the outmost two are in EPSG:3067, and the WMS GetMap was made with &CRS=EPSG:3067. The error is specific for the KKJ->ETRS-TM35FIN (EPSG:3067) transformation because if user reads the layer from WMS in EPSG:3857 then the middle tile stays where it should.

Unfortunately I do not have myself Mapserver with GDAL 3 and Proj 6 available for re-producing the error. If somebody wants to have a try it should be relatively easy. Edit the kkjtest.map mapfile and the "location" field of the kkjtest.shp to match with your file paths.

-Jukka Rahkonen- 

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