[GRASS5] PROJ_INFO and prime meridian

Paul Kelly paul-grass at stjohnspoint.co.uk
Wed Jun 4 15:16:54 EDT 2003

```Hello Markus
Below are a few ideas about the problem

On Wed, 4 Jun 2003, Markus Neteler wrote:

...
> Using the latest CVS version, I created a location with LCC:
> PROJ_INFO
> name: Lambert Conformal Conic
> towgs84: -104.1,-49.1,-9.9,0.971,-2.917,0.714,-11.68
> proj: lcc
> ellps: bessel
> a: 6377397.1550000003
> es: 0.0066743722
> f: 299.1528128000
> lat_0: 45.9000000000   <- given 45:54N

> lat_1: 33.0000000000   <- calculated by GRASS, given 'return'
> lat_2: 45.0000000000   <- calculated by GRASS, given 'return'

I am actually not sure this is right at all; you could try deleting these
two extra lines. I think lcc should have EITHER lat_0 OR (lat_1 AND lat_2)
but NOT all 3. In fact this looks like a bug in g.setproj as 33 and 45 are
the default values for lat_1 and lat_2 (in src/libes/gis/geo_init.c) and
have not been 'calculated'. Perhaps someone more familiar with the lcc
projection could comment.

> lon_0: 14.0000000000   <- given 14E
> x_0: 800000.0000000000
> y_0: 601000.0000000000
>
...
> Problems:
> - how to define a different prime meridian (monte Mario old/new)?

If the longitude of origin is given relative to the Monte Mario prime
meridian, then you would need to add the two together to give the
longitude of origin relative to Greenwich, i.e. 14d0 + 12d27'7.1 =
26d27'7.1"E Is this anywhere near the area covered by the map?

Or maybe the Monte Mario pm simply means the map is referenced to the
rome40 datum, in which case..

> - the towgs84 may be wrong (no idea what to use, I selected rome40)

these parameters would be right but the ellipsoid would be wrong, as
rome40 uses international. Is there some other reason it should be bessel?

...
> - Lambert Conic Orthomorphic != LCC (I hope not)

I think they are the same

> - the Gauss-boaga location with recent GIS data is wrong (I hope not)

If it also is rome40 does it use the same towgs84 parameters?

Paul

```