[GRASS-dev] status and updates of datumtransform.table

[Moritz Lennert]

What is the status of lib/gis/datumtransform.table ? Trying to do some 
reprojection between LL-WGS84 (epsg 4326) and belgian lambert 72 
(epsg:31370), I see some problems due to the parameters in that file:

- in the proj epsg file (Rel. 4.6.0, 21 Dec 2007), the belgian lambert 
72 projection is defined as

+proj=lcc +lat_1=51.16666723333333 +lat_2=49.8333339 +lat_0=90 
+lon_0=4.367486666666666 +x_0=150000.013 +y_0=5400088.438 +ellps=intl 
+towgs84=106.869,-52.2978,103.724,-0.33657,0.456955,-1.84218,1 +units=m 
+no_defs

- this is confirmed by the info given by the Belgian geographic 
institute [1], which gives the same parameters with only differences in 
sign of which I don't know if they have any effect

- however in lib/gis/datumtransform.table one can find:

bel72   "towgs84=-99.1,53.3,-112.5,0.419,-0.830,1.885,-1.00" "Belgium" 
"Accuracy about 0.3m"

which gives quite different results when reprojecting compared, for 
example, to cs2cs.

What is the reason to have this datumtransform.table file ? Isn't most 
of this covered by proj / epsg these days ?

Moritz

[1] http://www.ign.be/FR/FR2-1-2.shtm (bottom of the page)