id	summary	reporter	owner	description	type	status	priority	milestone	component	version	resolution	keywords	cc
105	EPSG 2391, 2392, 2393, 2394 and 3067 not working together without towgs84 parameters	pyrliu	warmerdam	"We had a major problem with our Lounaispaikka (http://www.lounaispaikka.fi/maakuntakaavat) map portal as most of our datasets are in Finland KKJ projections (epsg 2391, 2392 and 2933) displayed as layers on a basemap which is in ETRS-TM35FIN (epsg 3067) projection. Our OpenLayers map window is also in epsg:3067 and we are using Mapserver 5.6.6 on Ubuntu which relies on the /usr/share/proj/epsg library for projections.

All of the epsg:2391X based datasets where miss-projecting about 150-180 meters (screenshot attached) before Jukka Rahkonen from Tike advised us that we should include the +towgs84 parameters in the related epsg codes at the /usr/share/proj/epsg library.

All the projection problems where immediately corrected when the epsg codes where updated to the following:
# KKJ / Finland zone 1
<2391> +proj=tmerc +lat_0=0 +lon_0=21 +k=1 +x_0=1500000 +y_0=0 +ellps=intl +towgs84=-96.0617,-82.4278,-121.7435,4.80107,0.34543,-1.37646,1.4964 +units=m +no_defs <>
# KKJ / Finland zone 2
<2392> +proj=tmerc +lat_0=0 +lon_0=24 +k=1 +x_0=2500000 +y_0=0 +ellps=intl +towgs84=-96.0617,-82.4278,-121.7435,4.80107,0.34543,-1.37646,1.4964 +units=m +no_defs <>
# KKJ / Finland Uniform Coordinate System
<2393> +proj=tmerc +lat_0=0 +lon_0=27 +k=1 +x_0=3500000 +y_0=0 +ellps=intl +towgs84=-96.0617,-82.4278,-121.7435,4.80107,0.34543,-1.37646,1.4964 +units=m +no_defs <>
# KKJ / Finland zone 4
<2394> +proj=tmerc +lat_0=0 +lon_0=30 +k=1 +x_0=4500000 +y_0=0 +ellps=intl +towgs84=-96.0617,-82.4278,-121.7435,4.80107,0.34543,-1.37646,1.4964 +units=m +no_defs <>
# ETRS89 / ETRS-TM35FIN
<3067> +proj=utm +zone=35 +ellps=GRS80 +towgs84=0,0,0 +units=m +no_defs  <>

The +towgs84 parameters are based on spatialreference.org. These work like a charm as can now be seen from the second screenshot.

I'm adding this ticket as defect so that those who are agonizing with the same type of projection problems could find this information and resolve their problems by manually adding the +towgs84 parameters to the/usr/share/proj/epsg library. Note that the epsg:3067 +towgs84=0,0,0 was crucial for the projection problem to be corrected.

I'm also hoping that the +towgs84 parameters would be added to the distributed library for these epsg-codes in next version (4.8.0 ?) so that we can continue to receive updated through the wonderful world of apt and future proj-users in Finland would not have to suffer from projection errors.

Br. Pyry Liukas - Software Architect - Lounaispaikka"	defect	closed	minor	4.8.0	InitializationFiles	4.7.0	fixed	projection error problem towgs84 epsg mapserver	zumbrunn