[Proj] DHDN / Gauss Krueger to WGS84

[Oliver Eichler]

Hi Frank
> pjgaukru = pj_init_plus("+init=epsg:31467");
> pjwgs84 = pj_init_plus("+init=epsg:4326");
>
> //???
> double z = 0;
>
What is the z parameter for? Height?

>
> I would add that epsg:31467 expands as:
>
> +proj=tmerc +lat_0=0 +lon_0=9 +k=1.000000 +x_0=3500000 +y_0=0
> +ellps=bessel +datum=potsdam +units=m +no_defs
>
> Note that this definition is using +datum=potsdam which expands to:
>
>   +ellps=bessel +towgs84=606.0,23.0,413.0
>
That should be ok. These are maps from "Bayerisches
Landesvermessungsamt". Hope they know what they are doing.
> This may or may not be the best datum shift parameters for your area of
> work.  You may need to research a better local shift.
>
Does that mean that the shift parameters depend on the location within
the map? Or that the whole map might have some kind of bad offset
produced by a bad projection?

And how would I get better shift parameters? Is there a tutorial somewhere?

Thanks,

Oliver