[GRASSLIST:323] GRASS and the Norwegian coordinate systems (NGO48)

GRASS GRASS user
1

Hello list!

Can any of you answer me on this: Is it possible to use data in the Norwegian
coordinat system NGO48 (national grid for Norwegian maps, scale 1:1000 >
1:5000 in GRASS 5.x. (Maps from 1:50.000 and greater are normaly in UTM and
either Ed50 or WGS84/Euref89 - so no problem with those)). The system is
based on a Gauss-Krueger (Transversal Mercator) projection with a datum at
Oslo, based on a modified Bessel ellipsoid. Coordinates are x,y and z. X is
north-south (always positive), Y is positive towards east along the 58
degrees (latitude?), so we have negative cordinates West of Oslo. The system
operates with 8 axes (I-VIII).

-----------------------------------------------
Lars Forseth
Nord-Trøndelag Fylkeskommune
County Council of N-Troendelag
http://folk.uio.no/forseth
------------------------------------------------

2

Hello there

It looks like you will need to add the modified Bessel ellipsoid to the
ellipse.table file as it doesn't seem to be included. The file is in
$(GISBASE)/etc/ellipse.table, where $(GISBASE) is the directory GRASS is
installed in.

Add a line something like:

modif_bessel "Bessel Modified (Norway)" a=6377492.0176 f=1/299.15281285

to the end of the file and then run g.setproj, selecting 'tmerc' for the
projection and modif_bessel for the ellipsoid. The other parameters you
will need to answer the questions from g.setproj are at
http://crs.ifag.de/crs_national.php
There are actually 8 different co-ordinate systems, and if you have data
in different zones from I to VIII you will need to set up a separate GRASS
location for each zone.

If you are using the latest CVS version of GRASS then you would also be
able to take advantage of datum transformations between the WGS84 and
ngo48 datums. I will look at adding support for the ngo48 datum to the
GRASS CVS tomorrow, although you can always add it as a custom datum or
add the details to the datum.table and datumtransform.table files yourself
if you want, using the details at the above website.

In general it is possible to use almost any projection and datum in GRASS,
although some require a little more setting up than others. For European
countries most of the parameters you need are at
http://crs.ifag.de/crs_national.php, which is a very useful website.

I hope this is some help

Paul Kelly

3

On Mon, 9 Jun 2003, Lars Forseth wrote:

Hello list!

Can any of you answer me on this: Is it possible to use data in the Norwegian
coordinat system NGO48 (national grid for Norwegian maps, scale 1:1000 >
1:5000 in GRASS 5.x. (Maps from 1:50.000 and greater are normaly in UTM and
either Ed50 or WGS84/Euref89 - so no problem with those)). The system is
based on a Gauss-Krueger (Transversal Mercator) projection with a datum at
Oslo, based on a modified Bessel ellipsoid. Coordinates are x,y and z. X is
north-south (always positive), Y is positive towards east along the 58
degrees (latitude?), so we have negative cordinates West of Oslo. The system
operates with 8 axes (I-VIII).

If you look in the PROJ4 documentation, and look for a file for either
ESRI or EPSG, and search for Oslo, you get some references that look
familiar:

# NGO 1948 (Oslo)
<4817> +proj=longlat +a=6377492.018 +b=6356173.508712696
+towgs84=278.3,93,474.5,7.889,0.05,-6.61,6.21 +pm=oslo +no_defs no_defs
<>

for the longlat,

# NGO 1948 (Oslo) / NGO zone I
<27391> +proj=tmerc +lat_0=58 +lon_0=6.056250000000003 +k=1.000000 +x_0=0
+y_0=0 +a=6377492.018 +b=6356173.508712696
+towgs84=278.3,93,474.5,7.889,0.05,-6.61,6.21 +pm=oslo +units=m +no_defs
no_defs <>

and so on for the other zones. I don't know if this is precise enough,
though.

Roger

-----------------------------------------------
Lars Forseth
Nord-Trøndelag Fylkeskommune
County Council of N-Troendelag
http://folk.uio.no/forseth
------------------------------------------------

--
Roger Bivand
Economic Geography Section, Department of Economics, Norwegian School of
Economics and Business Administration, Breiviksveien 40, N-5045 Bergen,
Norway. voice: +47 55 95 93 55; fax +47 55 95 93 93
e-mail: Roger.Bivand@nhh.no

4

On Mon, 9 Jun 2003, Paul Kelly wrote:

ngo48 datums. I will look at adding support for the ngo48 datum to the
GRASS CVS tomorrow, although you can always add it as a custom datum or
add the details to the datum.table and datumtransform.table files yourself
if you want, using the details at the above website.

I have done this now; if you get the latest GRASS CVS version you can
create a new location and select ngo48 for the datum, choose the default set
of parameters for the datum transformation. The central parallel is 58,
central meridian for zone I should be entered in the format 06:03:22.5E
and similarly for the other 7 zones (details at
http://crs.ifag.de/country_select.php?country=NO ). For false easting,
false northing, scale on central parallel and units you can just select
the defaults and that should be it.

You can then r.proj, v.proj and s.proj your data between NGO48 locations
and the newer datum.

Paul K