[OSRS-PROJ] Roussilhe Oblique Stereographic

Paul Kelly paul-grass at stjohnspoint.co.uk
Mon Mar 15 11:34:56 EST 2004

On Mon, 15 Mar 2004 werchowyna at pf.pl wrote:

> Something propably stupid but let me know what you think:
> I suppose the "stere" projection is the closest match for Roussilhe. But the
> "stere" projection in "regular" Grass 5.03 doesn't ask for x_0 and y_0 which
> Roussilhe demands. This "stere" also asks for the "latitude of true scale"
> while the Roussilhe definition doesn't provide such parameter.
> So I MANUALLY made a PROJ_INFO like the one below. Would it work if I put it
> into my mapset (Grass 5.03 installed from an rpm provided by Mandrake on
> Mandrake 9.2)? Or is it completely rubbish?
> name: Stereographic
> datum:
> dx: 23.740000
> dy: -123.830000
> dz: -81.810000
> proj: stere
> ellps: krassovsky
> a: 6378245.0000000000
> es: 0.0066934216
> f: 298.3000000000
> lat_0: 51.6708333333
> lon_0: 16.6722222222
> x_0: 5467000
> y_0: 4637000
> k_0: 0.9998000000

Delete the empty datum: line and then this will work perfectly
(assuming the projection parameters are correct). Don't worry that GRASS
didn't ask you for some of the parameters. There is no definitive list of
the parameters for each projection (except in Gerald's head maybe! :) )
and GRASS just has a guess at prompting you for the correct ones but it
gets it wrong for some projections.

Make sure you have a PROJ_UNITS file as well (the one generated by g.setproj
should be OK).

You don't need the name: line but it does no harm. Also the lines
1. ellps: krassovsky
2. a: 6378245.0000000000
3. es: 0.0066934216
4. f: 298.3000000000
are partially redundant. Either 1 on its own, 2+3 or 2+4 will do fine.

Paul Kelly

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