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If ETRS89 (EPSG:4258) is tectonically fixed and WGS84 (EPSG:4326) isn't, the Helmert coefficients shouldn't be zero, right? In fact these parameters should diverge more and more with every new release of QGIS

I understand they're based on the same ellipsoid, but I think their central meridians are diverging, no? Why is the transformation (0,0,0,0,0,0,0)??

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  • which time period are you looking at?
    – Ian Turton
    Commented Sep 9, 2019 at 16:44
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    GIS people usually do not care. See github.com/OSGeo/PROJ/issues/571 ETRS89 IS a datum, also known as a reference frame. ETRS89 is defined to be alligned with WGS84 in the year 1989. Today the two references are off by around 70 cm (ETRS89 moves with the Eurasian plate, WGS84 does not). Historically the two frames have been viewed as equivalent in GIS, which is why the +towgs84 parameters are 0..
    – user30184
    Commented Sep 9, 2019 at 17:57
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    However, according to this presentation euref.eu/documentation/Tutorial2019/t-03-Hakli.pdf it is possible to deal with moving plates with current Proj library version. In that case user must know not only z, y, and z coordinates but time as well.
    – user30184
    Commented Sep 10, 2019 at 8:10

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The helmert coefficients between different implementation of ETRS89 [latest being ETRF2014] and ITRS implementation (latest being ITRF2020) can be found in this link. https://itrf.ign.fr/en/solutions/transformations

WGS84 is a geocentric datum much like the ITRF. The latest WGS84 implementation closely follows ITRF2014 implementation

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