[GRASS-dev] .g.proj datum_trans (5514)

[Martin Landa]

Hi,

2016-04-02 14:28 GMT+02:00 Martin Landa <landa.martin at gmail.com>:

> Adding `-t` flags leads to correct result.
>
> g.proj epsg=5514 datumt=2 -tp
> -PROJ_INFO-------------------------------------------------
> ...
> towgs84    : 570.8,85.7,462.8,4.998,1.587,5.261,3.56
> ...
>
> I don't know why `-t` flags is neeed here, selected parameters by
> `datumtrans` should be enough here.

I see, my proj library installation already defines `+towgs84` for EPSG 5514:

cat /usr/local/share/proj/epsg | grep 5514
<5514> +proj=krovak +lat_0=49.5 +lon_0=24.83333333333333
+alpha=30.28813972222222 +k=0.9999 +x_0=0 +y_0=0 +ellps=bessel
+towgs84=589,76,480,0,0,0,0 +units=m +no_defs  <>

I my eyes, when user defines `datumtrans` it should be enough (without
need to add also `-t` flag). I change it in r68205. So:

g.proj epsg=5514 datumt=2 -p
-PROJ_INFO-------------------------------------------------
...
towgs84    : 570.8,85.7,462.8,4.998,1.587,5.261,3.56
...

works.

Can anyone here explain when to use `-t` flag and it will make sense? Thanks. Ma

-- 
Martin Landa
http://geo.fsv.cvut.cz/gwiki/Landa
http://gismentors.cz/mentors/landa