[Proj] proj=undef ??

[support.mn at elisanet.fi]

Jose,

no it is not... "latlong" is defined as follows:

FORWARD(forward);
        xy.x = lp.lam / P->a;
        xy.y = lp.phi / P->a;
        return xy;
}

INVERSE(inverse);
        lp.phi = xy.y * P->a;
        lp.lam = xy.x * P->a;
        return lp;
}

it looks like they are multiplied by the major axis a.



I think what we needed for "nodef" is ...

FORWARD(forward);
        xy.x = lp.lam ;
        xy.y = lp.phi;
        return xy;
}

INVERSE(inverse);
        lp.phi = xy.y;
        lp.lam = xy.x;
        return lp;
}

Regards: Janne.

------------------------------------

Jose Gonçalves [jagoncal at gmail.com] kirjoitti: 
> Isn't the "undef" projection the same as "+proj=longlat"? You do a datum
> transformation of geographic coordinates with a command line as:
> 
> cs2cs +proj=longlat +ellps=bessel +towgs84=123,456,789 +to +proj=longlat
> +ellps=GRS80 +towgs84=1,2,3
> 
> Regards
> 
> Jose Gonçalves
> 
> 
> 
> 2011/6/23 <support.mn at elisanet.fi>
> 
> > Mikael,
> >
> > if the projection is "undef" then you can not enter any
> > projected points, since there is no known projection!
> >
> > But you can still enter latitudes and longitudes, and
> > that is exactly what people are doing.
> >
> > Janne.
> >
> > ----------------------------------
> >
> > Mikael Rittri [Mikael.Rittri at carmenta.com] kirjoitti:
> > > Janne, you wrote:
> > >
> > > > simply since you don't need any projection to do datum calculations.
> > >
> > > Do you mean that datum shifts can be done in longlat? True, but it
> > > was you who said that the coordinates were not in longlat but in
> > > some "undef" projection.  I though "undef" meant that you had no
> > > idea of how those coordinates are related to longlat.
> > >
> > > Let't take a concrete example:
> > >
> > > proj=undef
> > > ellps=bessel
> > > towgs84=123,456,789
> > > no_defs
> > >
> > > Now, I say that the input point is
> > >
> > > 53479811      97344703
> >
> > this is clearly a projected coordinate since
> > the values are  too large to be lat or lon. As
> > said if the proj="undef" then the coordinates
> > are passed through and are earth angular
> > (lat and lon).
> >
> > You should here enter:
> >
> > 65.12312N 34.56W
> >
> > for example.
> >
> > >
> > > Can you tell me how this point could possibly be translated to
> > >
> > > proj=undef
> > > datum=WGS84
> > >
> >
> > With datum shift that might give output such as:
> > 65.2342N 34.52344W
> >
> > > Or maybe you can tell me under what circumstances you want to
> > > use such a feature?
> > >
> >
> > Many point file formats give values earth angular (lat and lon) and
> > never bother to project them to anything. They can still be datum shifted
> > but mostly in WGS84 nowadays.
> >
> > My idea is that it is better to let the proj.4 library to handle this case
> > than
> > to program an additional layer over it just to check if the projection is
> > undef and do nothing in that case.
> >
> > So as the proj.4 library now can short circuit the case when one of the
> > datums is "undef" it should also be able to short circuit the case when
> > one of the projections is "undef" and it should pass all the values from
> > input to output assuming that the projection (or inverse projection) is
> > not required.
> >
> > This feature would not affect any other calculations and mechanisms at
> > all it is just a short cut.
> >
> > Janne.
> >
> > _______________________________________________
> > Proj mailing list
> > Proj at lists.maptools.org
> > http://lists.maptools.org/mailman/listinfo/proj
> >
> 
> _______________________________________________
> Proj mailing list
> Proj at lists.maptools.org
> http://lists.maptools.org/mailman/listinfo/proj