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In QGIS I can choose among other things between "ETRS89 / ETRS-TM32" and "ETRS89 / UTM zone 32N". In my test project both projections displayed the layers at the very same place. So, where is the difference?

The proj4 codes are
+proj=utm +zone=32 +ellps=GRS80 +towgs84=0,0,0,0,0,0,0 +units=m +no_defs
+proj=utm +zone=32 +ellps=GRS80 +towgs84=0,0,0,0,0,0,0 +units=m +vunits=m +no_defs

What does +vunits=m mean?

  • vertical unit is the meter. I think ETRS-TM32 has axis order of northing, then easting, but it's unclear from the EPSG registry. What are the WKIDs / codes associated with these two CRS? – mkennedy Sep 30 '14 at 16:23
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    @mkennedy: EPSG codes are 3044 and 25832 without +vunits and 5555, 5972, 6172 and 7416 with +vunits. I don't see any difference in the other projection parameters. – AndreJ Sep 30 '14 at 17:40
  • @AndreJoost It looks like QGIS ignores axis ordering like ArcGIS does! But it could make a difference if the data is used later in other software. Only 3044 has the northing-easting axis ordering. – mkennedy Sep 30 '14 at 18:14
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+vunits=m is for vertical datums.

Since QGIS is still two-dimensional, it has no impact on the projection.

For more details, see http://trac.osgeo.org/proj/wiki/VerticalDatums and

http://osgeo-org.1560.x6.nabble.com/Vertical-and-geocentric-coordinate-support-in-OGR-PROJ4-td3841151.html

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