Re: Fwd: Re: 20040322: Any idea why gribtocdl does a "floating exception" on this file?

• To: Rich Signell <rsignell@xxxxxxxxx>
• Subject: Re: Fwd: Re: 20040322: Any idea why gribtocdl does a "floating exception" on this file?
• From: Robb Kambic <rkambic@xxxxxxxxxxxxxxxx>
• Date: Thu, 8 Apr 2004 14:34:18 -0600 (MDT)

Rich,

The cdl file is attached, it only has the true lat/lon for the 1st and the
last point. As I said before the calculations had too many rounding errors
or something. If you really need all those coordinates, you could create
them using MATLAB and then enter them into the cdl. It's only a text file.
Using  gribtonc to decode grib.3, it created a correct netcdf file. Hope
this helps. Been in meetings for the last couple of days.

Robb...




On Fri, 2 Apr 2004, Rich Signell wrote:

Robb,

Yes, my calcs were done using doubles (Matlab uses
doubles by default).

-Rich

--- Robb Kambic <rkambic@xxxxxxxxxxxxxxxx> wrote:
> 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
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> use: APO AE 09613-5000
> > > >
> > > >
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=== message truncated ==


====
Rich Signell
work: signell@xxxxxxxxxxxxxxxxx
home: signell@xxxxxx

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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/
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