[Proj] Difference between Proj4 datums and EPSG database

[Markus Neteler]

On Tue, Nov 28, 2006 at 12:34:08PM -0500, Frank Warmerdam wrote:
...
> This does not have any TOWGS84 parameters associated with the datum
> Deutsches_Hauptdreiecksnetz, presumably because EPSG publishes more than
> one possible solution though I'd have to do some digging to verify that.

Frank,

if this help: In GRASS we have a list of 'potsdam' datums,
with 3 and 7 parameters:

cd lib/gis/
datum.table:
# Potsdam Rauenberg 1950 DHDN
potsdam "Deutsches_Hauptdreiecksnetz"         bessel        dx=606.0    dy=23.0     dz=413.0

datumtransform.table:
# http://crs.ifag.de/
potsdam "towgs84=612.4,77.0,440.2,-0.054,0.057,-2.797,2.55" "Germany (Sachsen)" "Accuracy <1m"
potsdam "towgs84=599.4,72.4,419.2,-0.063,-0.022,-2.723,6.46" "Germany (Thüringen)""Accuracy <1m"
potsdam "towgs84=590.5,69.5,411.6,-0.796,-0.052,-3.601,8.30" "Germany (West - North - 52d20'N to 55d00'N)" "Accuracy <1m"
potsdam "towgs84=584.8,67.0,400.3,0.105,0.013,-2.378,10.29" "Germany (West - Middle - 50d20'N to 52d20'N)" "Accuracy <1m"
potsdam "towgs84=597.1,71.4,412.1,0.894,0.068,-1.563,7.58" "Germany (West - South - 47d00N to 50d20'N)" "Accuracy <1m"
potsdam "towgs84=598.1,73.7,418.2,0.202,0.045,-2.455,6.70" "Germany (Whole Country)" "Accuracy 3m"

GRASS shows the list to the user to select from.

Best regards,
Markus