[Proj] Ukraine towgs84

[Clifford J Mugnier]

Oscar,

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.

C. Mugnier
LSU

> From: Maciek Sieczka <werchowyna-epf.pl>

> So far we have found a Mapinfo towgs84 definition claimed to be suitable
> for Ukraine: 24,-123,-94,-0.02,0.25,0.13,1.1.
>
> Although it yields pretty different results than the pan-Soviet Union
> datum shift, I only have the word of Mapinfo authors that it is correct.
>
> Input is WGS84 23E 49N.
>
> Results:
> former Soviet Union datum shift (28,-130,-95)
> 23d00'06.425689"E       49d00'01.319468"N
>
> Mapinfo Ukrainian (24,-123,-94,-0.02,0.25,0.13,1.1)
> 23d00'05.992369"E       49d00'01.513576"N

Inspecting the EPSG database I found the latter parameters under coordinate
operation codes 1310, 1674, 1675. For these the area-of-use code is 1343
and
this leads to East-Germany!
Looking in the EPSG area-of-use table there are several entries for Ukraine
and one specifically for Ukraine is number 1242. Oddly, no coordinate
operation nor CRS uses this area code in the EPSG database.

Another remark: if you take the mentioned parameters for a datum transform
in the Ukraine, then you should check the signs. It is possible that you
used the right signs just by chance.
The EPSG database gives under coordinate operation code 1310 the parameters
for Pulkovo 42 / Krasovskij to ETRS89.
dx=24; dy=-123; dz=-94; rx=-0.02; ry=0.25; rz=0.13; ds=1.1;
These parameters are for the coordinate frame method (code 9607) in the
direction Pulkovo -> ETRS89.
The correct signs for the position vector method in the opposite direction:
dx=-24; dy=123; dz=94; rx=-0.02; ry=0.25; rz=0.13; ds=-1.1;
PROJ.4 uses the (approximated) position vector method (coordinate operation
code 9606).

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

Note that the used transformation parameters seem to be the wrong ones for
Ukraine, according to EPSG.

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