[Proj] Ukraine towgs84

Oscar van Vlijmen ovv at hetnet.nl
Wed Dec 7 01:41:22 EST 2005

> From: Clifford J Mugnier <cjmce-lsu.edu>

> An ellipsoid height that is negative is not necessarily "meaningless."  For
> a sea-level elevation of zero meters, EVERYWHERE in the Continental United
> States the ellipsoid height is -26 to -27 meters.  It may look "funny," but
> that's what it really is - the separation between the ellipsoid and the
> geoid.


> With an assumed height of zero, I arrive at the following coordinates (lat,
> lon):
> 49d 00m 01.03814s, 23d 00m 06.07119s
> and a meaningless height of -28.58 m

Perfectly meaningless in this case I'm inclined to believe, because in the
original data no height was provided. The usual way is then to assume a
height of zero, which gives after transformation a meaningless number.
It has some other relevant meaning however. Since most 3D transformations
are highly sensitive to the height parameter, it's a good check for
comparing calculations!

By the way, the EGM96 geoid height on the WGS84 ellipsoid can be calculated
(The URL changes every year or so.)
For WGS84 lat, lon 49, 23 the calculator gives a geoid height of 36.71 m.

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