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<p>Hi list members -</p>
<p>I have question regarding coordinate reference systems.</p>
<p>As I understand the difference between the datums WGS84 and
ETRS89:</p>
<ul>
<li>They are based on the same ellipsoid. And in 1989 there were -
for all practical purposes - <i>no</i> difference between the
the 2 datums coordinate wise<br>
</li>
<li>However, the datums are "drifting" apart because the ETRS89 is
coordinate bound to the Eurasian continental plate and WGS84 is
not. <br>
</li>
<li>The continental drift is ca 2.5 cm / year. And around 70 cm in
all.</li>
</ul>
<p>So a specific position in Denmark (or Europe) in the same
mathematical projection i.e UTM32N should have 2 <i>different</i>
x,y values using the WGS84 datum and ETRS89 datum. And the
present "distance" should be ca. 70 cm. <br>
</p>
<p>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.</p>
<p>(Doing the same experiment using ED50 instead of WGS84 show the
expected difference around 200 m between ED50 and ETRS89) <br>
</p>
<p>How come ? Or is the error-source sitting ca. 70 cm in front of
the screen ?? (I have a 34" large flatscreen :-) <br>
</p>
<p> <br>
</p>
<pre class="moz-signature" cols="72">--
Med venlig hilsen / Kind regards
Bo Victor Thomsen
</pre>
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