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On Thu, 1 Apr 2004, Richard Signell wrote:
Robb, I can't believe I didn't notice this before, but you are using pole_lat, pole_lon = (-32.5, 10) but for the rtll formula I gave you to produce the right results I was using pole_lat, pole_lon = (57.5, 10) which yields true lon/lat domain LL and UR corners: lon(1,1)=4.5337 lat(1,1)=33.2988 lon(272,234)=24.6762 lat(272,234)=49.4020
Rich, The lats/lons are almost correct now, but I have some round-off error. The first one is correct la1 =-24, lo1 = -5 lon_true[ 1, 1 ] =4.53367311069887, lat_true[ 1, 1 ] =33.2987847224989 if I plug in the following values, then I get the same answers you did. la2 =-7.063, lo2 = 9.563 lon_true[ 2, 2 ] =24.67621972076, lat_true[ 2, 2 ] =49.401952455077 But iterations has round-off lon[ 234 ] =10.269655932, lat[ 272 ] =-6.240013916 lon_true[ 234, 272 ] =26.0203076954498, lat_true[ 234, 272 ] =50.0461679747345 Next, I going to try doubles instead of floats. Robb...
See attached image.
So I guess either you need to insert a:
pole_lat=90-pole_lat;
line before you use my rtll formula, or else DWD have
incorrectly specified the "pole_lat" as 90-"pole_lat" in the grib file.
-Rich
Robb Kambic wrote:
>
> On Tue, 30 Mar 2004, Richard Signell wrote:
>
> > Robb Kambic wrote:
> > >
> > > Rich,
> > >
> > > I have the formulas needed but the results don't seem correct to me. The
> > > pole is lat/lon (-32.5, 10). So ( -24, -5 ) -> ( -32.5, 10 ) and
> > > (-7,063, 9.563 ) -> ( -15.563, 24.563 ) Since the rotation angle is 0,
> > > there is no rotation. The lat/lon increment is .065535004
> > >
> > > The problem is the calculated corner from the starting point of
> > > ( -32.5, 10 ) ends up at ( -17.23, 27.76 ) instead of the given one
> > > ( -15.563, 24.563 ). It's a couple of degrees off. I don't think it's a
> > > rounding err, so I must be missing something.
> > >
> >
> >
> > I think I see your problem. In the rotated pole coordinate, the grid
> > is uniformly spaced in lat/lon, but in the rotated pole coordinate,
> > it *is not*. You therefore need 2D arrays to hold the true lon/lat
> > values, and you need to compute each of these values using the formula.
>
> Rich,
>
> OK, I duplicated the code and the results still are not correct. ie
>
> should be lon= 24.563 and lat = -15.563
>
> straight increment, had error in first calculation
> lon[ 234 ] = 25.269655932, lat[ 272 ] = -14.7400139159998
>
> results from duplicated rtll
> almd=44.4907691654722, aphd=-43.1948333734209
>
> How about you send the lat lon values thru MatLab and see what values you
> get for the ending coordinates.
>
> Robb..
>
> >
> > In other words, you need to loop thru each grid point(e.g.):
> >
> > for j=1:272
> > lat=lat(j);
> > for i=1:234
> > lon=lon(i)
> > [lon_true(i,j),lat_true(i,j)]=rtll(pole_lon,pole_lat,lon(i),lat(i));
> > end
> > end
> >
> > and lon_true, lat_true will be 2D arrays:
> >
> > lon_true(lat,lon)
> > lat_true(lat,lon)
> >
> >
> > > On Mon, 29 Mar 2004, Richard Signell wrote:
> > >
> > > > Robb,
> > > >
> > > > If it's helpful, here is my MATLAB function for deriving true lon,lat
> > > > from the rotated pole lon,lat.
> > > >
> > > > function [almd,aphd]=rtll(tlm0d,tph0d,tlmd,tphd);
> > > >
%-------------------------------------------------------------------------
> > > > % RTLL transforms rotated coordinates (tlmd,tphd) into
> > > > % ordinary geographic coordinates (almd,aphd). i/o decimal degrees (DD)
> > > > % tlm0d, tph0d: lon e lat of the center of rotation ("North Pole") in
> > > > DD.
> > > > %
> > > > dtr=pi/180.;
> > > >
> > > > ctph0=cos(tph0d*dtr);
> > > > stph0=sin(tph0d*dtr);
> > > >
> > > > stph=sin(tphd*dtr);
> > > > ctph=cos(tphd*dtr);
> > > > ctlm=cos(tlmd*dtr);
> > > > stlm=sin(tlmd*dtr);
> > > >
> > > > aph=asin(stph0.*ctph.*ctlm+ctph0.*stph);
> > > > cph=cos(aph);
> > > >
> > > > almd=tlm0d+asin(stlm.*ctph./cph)/dtr;
> > > > aphd=aph/dtr;
> > > > % end
> > > >
> > > >
> > > > -Rich
> > > >
> > > >
> >
> > --
> > Dr. Richard P. Signell | signell@xxxxxxxxxxxxxxxxx
> > NATO/SACLANT Undersea Research Centre | Tel: (+39) 0187 527 381
> > Viale San Bartolomeo 400 | Fax: (+39) 0187 527 331
> > 19138 La Spezia, ITALY --> From USA/CANADA, use: APO AE 09613-5000
> >
> >
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> >
>
> ==============================================================================
> Robb Kambic Unidata Program Center
> Software Engineer III Univ. Corp for Atmospheric Research
> rkambic@xxxxxxxxxxxxxxxx WWW: http://www.unidata.ucar.edu/
> ==============================================================================
--
Dr. Richard P. Signell | signell@xxxxxxxxxxxxxxxxx
NATO/SACLANT Undersea Research Centre | Tel: (+39) 0187 527 381
Viale San Bartolomeo 400 | Fax: (+39) 0187 527 331
19138 La Spezia, ITALY --> From USA/CANADA, use: APO AE 09613-5000
***PRIVILEGED AND CONFIDENTIAL***
The information contained in this e-mail message (including any attached files)
is intended for the use of the addressee(s) only and is priviliged information.
The information should neither be posted to the Internet, nor published in any
other public domain, without the express permission of the sender. If you are
not the intended recipient(s) or the recipient's representative, you are hereby
notified that any use, disclosure, copying or distribution of this
communication is prohibited. If you have received this communication in error
please notify us immediately at postmaster@xxxxxxxxxxxxxxxxx, and remove this
message from your system.
============================================================================== Robb Kambic Unidata Program Center Software Engineer III Univ. Corp for Atmospheric Research rkambic@xxxxxxxxxxxxxxxx WWW: http://www.unidata.ucar.edu/ ==============================================================================
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