[Proj] forward/inverse projection logic for ob_tran
Davide Cesari
dcesari at arpa.emr.it
Mon Oct 10 02:54:14 EST 2011
Il -10/01/-28163 20:59, Hermann Peifer ha scritto:
> Hi,
>
> I am currently dealing with regional climate models, where the data
> comes in form of "rotated pole lat/lon grids", with the North Pole at
> 39.25N, 162W.
>
> I am able to convert "rotated pole coordinates" to "normal lat/lon
> coordinates" by using:
>
> $ proj -f "%.6f" -m 57.2957795130823 +proj=ob_tran +o_proj=latlon
> +o_lon_p=-162 +o_lat_p=39.25 +lon_0=180
>
> It looks to me that the proj/invproj (i.e. forward/inverse) projection
> logic is opposite to what I would expect: I need to run proj (i.e. the
> forward projection) in order get from the "rotated lat/lon" coordinates
> (say: lon=0,lat=0) back to the "normal lat/lon coordinates" (here:
> lon=18.0,lat=50.75), and vice versa.
>
> Is this expected behaviour? If yes: what am I missing?
>
> Thanks for your time, Hermann
Hi Hermann, thank you the message, I had also raised the problem some
time ago, see e.g. this message in the proj mail archive:
http://osgeo-org.1803224.n2.nabble.com/Re-rotated-pole-ob-tran-help-needed-td5149504.html
but there was not much reaction, I think the problem is simply that the
use of this kind of rotation in Numerical Weather Prediction models and
in Cartography is the opposite. Maybe an additional set of switches
could be added to the ob_tran transform in order to get the expected (by
us) behavior, unfortunately I have no time to dedicate to that at the
moment, but I would like to do it if there is a chance that it will be
accepted in the main proj code.
best regards, Davide
--
============================= Davide Cesari ============================
Servizio IdroMeteoClima - ARPA Emilia Romagna
NWP modelling - Modellistica numerica previsionale
Phone/Fax: +39 051525926/+39 0516497501
E-mail: dcesari at arpa.emr.it
Home page: http://www.webalice.it/o.drofa/davide/
Address: ARPA-SIM, Viale Silvani 6, 40122 Bologna, Italy
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