[Proj] old german topo

[Maciek Sieczka]

From: "John Smart" <john.smart at caris.com>

> Here are the results of a couple of test runs of the proj program, using
> Gauss-Krueger projection and Bessel ellipsoid, zone 5:
> (...)
> Looks like pretty reasonable correspondence to what's on your map.
> Gauss-Krueger zone 5, central meridian 15 east, false easting 5500000,
> scale factor = 1.

Thanks! I tried it and appears allright. I registered the Mestichblatter map
using Grass 5.3 into the projection above with all the grid crossings (121
points), exported into tiff/tfw, reprojected into the Polish "System 92"
(tmerc on GRS80) using gdalwarp and imported it into Grass mapset with a
"System 92" 1:10000 topo.When the Mestichblatter is displayed over the
"System 92" map it looks quite in sync but there are differences of about
3-15m in the location of even churches and few other buildings which I
don't suppose to have moved. I can't see a clear tendency in these
differences,
they are in different directions. Do you think the projection used may not
be the proper one? Or maybe I expect too much? I mean the map was prepared
in '30s and it's only 1:25000 so it can't be any more accurate propably (?).

As to the datums I tried 3 different ones and I'm not sure which one is
really suitable here. I believe I had a best result with the first of the
mentioned below. Though the reprojection result was very similar in each
case (max 1-2 m difference) I would like to know which one is right if
somebody can tell me.

1. +towgs84=584.8,67.0,400.3,0.105,0.013,-2.378,10.29
taken from the
http://crs.bkg.bund.de/crseu/crs/descr/eu-countrysel.php?country=DE ->
DE_DHDN / GK_3 -> Transf. -> DE_DHDN (Middle) to ETRS89

2. +towgs84: 597.1,71.4,412.1,0.894,0.068,-1.563,7.58
GRASS 5.3, datum: potsdam

3. +towgs84=606.0,23.0,413.0
GDAL 1.2.0, potsdam bessel, Potsdam Rauenberg 1950 DHDN

Maciek