Hi list members -
I have question regarding coordinate reference systems.
As I understand the difference between the datums WGS84 and ETRS89:
* They are based on the same ellipsoid. And in 1989 there were - for
all practical purposes - /no/ difference between the the 2 datums
coordinate wise
* However, the datums are "drifting" apart because the ETRS89 is
coordinate bound to the Eurasian continental plate and WGS84 is not.
* The continental drift is ca 2.5 cm / year. And around 70 cm in all.
So a specific position in Denmark (or Europe) in the same mathematical
projection i.e UTM32N should have 2 /different/ x,y values using the
WGS84 datum and ETRS89 datum. And the present "distance" should be ca.
70 cm.
However, that is not the case in QGIS (v. 3.8): A point digitized with
position (550000, 6080000) in ETRS89/UTM32N has the (almost) exact same
x/y values in WGS84/UTM32N when you change the projection in the map
window from ETRS89/UTM32N to WGS84/UTM32N. The x/y values differs around
.1 mm. Certainly no "drift" around 70 cm.
(Doing the same experiment using ED50 instead of WGS84 show the expected
difference around 200 m between ED50 and ETRS89)
How come ? Or is the error-source sitting ca. 70 cm in front of the
screen ?? (I have a 34" large flatscreen :-)
--
Med venlig hilsen / Kind regards
Bo Victor Thomsen
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