[GRASS5] New Datums

[Paul Kelly]

On Tue, 27 May 2003, Markus Neteler wrote:

> What I would like to see in 5.0.3:
> - the new PROJ4 related code with datum transformation

We need to tidy up the datum names used in GRASS before doing this. I
don't know where they came from but some are a bit dubious. I would like
to use the Open GIS Consortium Well-known Text values (OGC WKT) for the
long descriptive names for the datums, to make it easier to output the
projection information to other GIS. Here is a summary of the names in
GRASS and what I think the OGC name is:

I am fairly sure about these ones:
wgs84  "World_Geodetic_System_1984"  wgs84
wgs72  "World_Geodetic_System_1972"  wgs72
nad27  "North_American_Datum_1927"  clark66
nad83   "North_American_Datum_1983"  grs80
osgb36 "OSGB_1936" airy
tokyo  "Tokyo"                       bessel
sam69 "South_American_Datum_1969"               sam69
eur50   "European_Datum_1950"             international
agd66   "Australian_Geodetic_Datum_1966"          australian
agd84   "Australian_Geodetic_Datum_1984"          australian
rome40  "Monte_Mario"         international
S-42    "Pulkovo_1942"            krassovsky
potsdam "Deutsches_Hauptdreiecksnetz"     bessel
carthage "Carthage"               clark80

But not these ones
The 4 below seem to all be duplicate entries. Some had separate sets of
parameters (which are now handled by the datumtransform.table file).

a-can  "Please use nad27 instead"         clark66
aus    "Please use agd66 instead"              australian
SAD-69  "Please use sam69 instead"        sam69
pulkovo "Please use S-42 instead"         krassovsky

I decided on using S-42 instead of pulkovo as the abbreviation for the
last one, partly because it included the year and partly because Pulkovo
may be spelt wrongly but maybe it is just an anglicisation of the
placename (as in rome40 instead of roma40). Now I'm not as sure what it
should be called.

I don't know what these ones correspond to---anybody any ideas or should I
delete them?
eur    "European"                         international
eur79   "European 1979 mean"              international
grs80   "Geographic Reference System 1980" wgs84
Sasia   "South Asia"                      fschr60m

As far as I was aware grs80 is an ellipsoid and not a datum; it is
implemented as a datum in nad83 in America and etrs89 in Europe.

hermannskogel "Militar_Geographische_Institut"    bessel

Hermannskogel seems to be in Austria so this name seemed appropriate but
there is also S_JTSK_Ferro which applies to the Czech Republic and
Slovakia, but are these the same datum?


Below here are ones I have added

ire65    "TM65"                   modif_airy
ch1903   "CH1903"     bessel
ntf87    "Nouvelle_Triangulation_Francaise"                    plessis
etrs89   "European_Terrestrial_Reference_System_1989"   grs80
bel72    "Reseau_National_Belge_1972"             international
lis37    "Lisbon_1937"    international


And here are some new ones I found reference to at http://crs.ifag.de/ but
don't know what the official name should be. Can anybody help?

rd18     "Rijksdriehoeks Datum 1918 (Netherlands)" bessel
por73    "Portuguese Datum 1973"          international
hjors55  "Hjorsey 1955 (Iceland)"         international

Another point is that it was very hard to find transformation parameters
for France (I tried to add support for a few European countries but of
course it is not complete). The above website only had one 3-parameter
transformation for the whole of France which couldn't be very accurate.
And there should be more countries there as well but it takes quite a
while to research the parameters and even then I can't test if they are
correct.


Paul