netcdf rotated lat-lon grid
Varlamv Sergey
vsm at RIAM.KYUSHU-U.AC.JP
Wed May 28 00:43:44 EDT 2008
Benry,
To plot your data in the lon-lat space
you could use the 'PDEF' feature of
GrADS that will enable grads to interpolate
your data 'on the fly'.
The official version of GrADS (both 1.9 and 2.0)
had a bug that prevented PDEF to work correctly
with the NetCDF data.
Couple of weeks ago I suggested and submitted
the bug correction for GrADS code to the GrADS team.
If you are able to compile GrADS - I will send to you directly
this correction. It makes possible to visualize the NetCDF data with PDEF
support if data are saved in the 'standard' t,z,y,x order. Yours are.
For me now GrADS perfectly plots the
ocean data originally in the curvilinear ORCA grid.
However, using PDEF would require from you
some programming effort on the way to construct
the PDEF files for your case, but just once.
Best regards,
Sergey Varlamov
Berny Bisselink wrote:
> Hi GrADS users,
> I am trying to read a NetCDF data file with a rotated lat-lon grid.
> The ncdump file is as follows:
>
> netcdf precip.KNMI-2003.ENS50.RT3 {
> dimensions:
> rlon = 114 ;
> rlat = 124 ;
> gsize2 = 2 ;
> height = 1 ;
> time = UNLIMITED ; // (365 currently)
> tbnds = 2 ;
> variables:
> float rlon(rlon) ;
> rlon:long_name = "rotated longitude" ;
> rlon:units = "degrees" ;
> float rlat(rlat) ;
> rlat:long_name = "rotated latitude" ;
> rlat:units = "degrees" ;
> float height(height) ;
> height:long_name = "height above the surface" ;
> height:units = "m" ;
> double time(time) ;
> time:bounds = "time_bnds" ;
> time:units = "days since 1950-01-01 00:00" ;
> time:calendar = "365_day" ;
> double time_bnds(time, tbnds) ;
> time_bnds:units = "days since 1950-01-01 00:00" ;
> time_bnds:calendar = "365_day" ;
> float lon(rlat, rlon) ;
> lon:long_name = "longitude" ;
> lon:units = "degrees_east" ;
> float lat(rlat, rlon) ;
> lat:long_name = "latitude" ;
> lat:units = "degrees_north" ;
> float dir(rlat, rlon) ;
> dir:long_name = "angle of rotation" ;
> dir:units = "degrees" ;
> int date_bnds(time, gsize2) ;
> date_bnds:long_name = "Verifying Date at Start and Finish
> of Interval" ;
> date_bnds:units = "yyyymmdd" ;
> int hms_bnds(time, gsize2) ;
> hms_bnds:long_name = "Verifying Hour-Minute-Second at Start
> and Finish of Interval" ;
> hms_bnds:units = "hhmnss" ;
> float precip(time, height, rlat, rlon) ;
> precip:long_name = "Total Precipitative Flux" ;
> precip:standard_name = "precipitation_flux" ;
> precip:units = "kg m-2 s-1" ;
> precip:cell_methods = "time: 24-hr averaged values" ;
> precip:grid_mapping_name = "rotated_latitude_longitude" ;
>
> // global attributes:
> :CDI = "Climate Data Interface version 1.1.0" ;
> :Conventions = "CF-1.0" ;
> :history = "Fri Apr 18 17:20:35 2008: cdo -r selyear,2003
> precip.KNMI-2001.ENS50.RT3.nc precip.KNMI-2003.ENS50.RT3.nc" ;
> :Source = "RACMO2" ;
> :Domain = "ENS50" ;
> :Experiment = "RT3" ;
> :Institution = "KNMI" ;
> :CreationDate = "Sat Nov 4 23:38:30 2006" ;
> :CDO = "Climate Data Operators version 1.1.0 available from
> http://www.mpimet.mpg.de/cdo" ;
> data:
>
> rlon = -28.21, -27.77, -27.33, -26.89, -26.45, -26.01, -25.57, -25.13,
> -24.69, -24.25, -23.81, -23.37, -22.93, -22.49, -22.05, -21.61, -21.17,
> -20.73, -20.29, -19.85, -19.41, -18.97, -18.53, -18.09, -17.65, -17.21,
> -16.77, -16.33, -15.89, -15.45, -15.01, -14.57, -14.13, -13.69, -13.25,
> -12.81, -12.37, -11.93, -11.49, -11.05, -10.61, -10.17, -9.73, -
> 9.289999,
> -8.849999, -8.409999, -7.969999, -7.529999, -7.089999, -6.649999,
> -6.209999, -5.769999, -5.329999, -4.889999, -4.449999, -4.009999,
> -3.569999, -3.129999, -2.689999, -2.249999, -1.809999, -1.369999,
> -0.9299992, -0.4899992, -0.04999924, 0.3900008, 0.8300008, 1.270001,
> 1.710001, 2.150001, 2.590001, 3.030001, 3.470001, 3.910001, 4.350001,
> 4.790001, 5.23, 5.670001, 6.110001, 6.550001, 6.990001, 7.430001,
> 7.870001, 8.31, 8.750001, 9.190001, 9.630001, 10.07, 10.51, 10.95,
> 11.39,
> 11.83, 12.27, 12.71, 13.15, 13.59, 14.03, 14.47, 14.91, 15.35, 15.79,
> 16.23, 16.67, 17.11, 17.55, 17.99, 18.43, 18.87, 19.31, 19.75, 20.19,
> 20.63, 21.07, 21.51 ;
>
> rlat = -26.73, -26.29, -25.85, -25.41, -24.97, -24.53, -24.09, -23.65,
> -23.21, -22.77, -22.33, -21.89, -21.45, -21.01, -20.57, -20.13, -19.69,
> -19.25, -18.81, -18.37, -17.93, -17.49, -17.05, -16.61, -16.17, -15.73,
> -15.29, -14.85, -14.41, -13.97, -13.53, -13.09, -12.65, -12.21, -11.77,
> -11.33, -10.89, -10.45, -10.01, -9.57, -9.129999, -8.69, -8.25,
> -7.809999, -7.37, -6.93, -6.49, -6.05, -5.61, -5.17, -4.73, -4.289999,
> -3.85, -3.41, -2.97, -2.53, -2.09, -1.65, -1.21, -0.7699997, -
> 0.3299997,
> 0.1100003, 0.5500003, 0.9900003, 1.43, 1.87, 2.31, 2.75, 3.19, 3.63,
> 4.07, 4.51, 4.95, 5.39, 5.83, 6.27, 6.71, 7.15, 7.59, 8.030001, 8.47,
> 8.91, 9.35, 9.79, 10.23, 10.67, 11.11, 11.55, 11.99, 12.43, 12.87,
> 13.31,
> 13.75, 14.19, 14.63, 15.07, 15.51, 15.95, 16.39, 16.83, 17.27, 17.71,
> 18.15, 18.59, 19.03, 19.47, 19.91, 20.35, 20.79, 21.23, 21.67, 22.11,
> 22.55, 22.99, 23.43, 23.87, 24.31, 24.75, 25.19, 25.63, 26.07, 26.51,
> 26.95, 27.39 ;
>
> height = 0 ;
>
> time = 19345, 19346, 19347, 19348, 19349, 19350, 19351, 19352, 19353,
> 19354,
> 19355, 19356, 19357, 19358, 19359, 19360, 19361, 19362, 19363, 19364,
> 19365, 19366, 19367, 19368, 19369, 19370, 19371, 19372, 19373, 19374,
> 19375, 19376, 19377, 19378, 19379, 19380, 19381, 19382, 19383, 19384,
> 19385, 19386, 19387, 19388, 19389, 19390, 19391, 19392, 19393, 19394,
> 19395, 19396, 19397, 19398, 19399, 19400, 19401, 19402, 19403, 19404,
> 19405, 19406, 19407, 19408, 19409, 19410, 19411, 19412, 19413, 19414,
> 19415, 19416, 19417, 19418, 19419, 19420, 19421, 19422, 19423, 19424,
> 19425, 19426, 19427, 19428, 19429, 19430, 19431, 19432, 19433, 19434,
> 19435, 19436, 19437, 19438, 19439, 19440, 19441, 19442, 19443, 19444,
> 19445, 19446, 19447, 19448, 19449, 19450, 19451, 19452, 19453, 19454,
> 19455, 19456, 19457, 19458, 19459, 19460, 19461, 19462, 19463, 19464,
> 19465, 19466, 19467, 19468, 19469, 19470, 19471, 19472, 19473, 19474,
> 19475, 19476, 19477, 19478, 19479, 19480, 19481, 19482, 19483, 19484,
> 19485, 19486, 19487, 19488, 19489, 19490, 19491, 19492, 19493, 19494,
> 19495, 19496, 19497, 19498, 19499, 19500, 19501, 19502, 19503, 19504,
> 19505, 19506, 19507, 19508, 19509, 19510, 19511, 19512, 19513, 19514,
> 19515, 19516, 19517, 19518, 19519, 19520, 19521, 19522, 19523, 19524,
> 19525, 19526, 19527, 19528, 19529, 19530, 19531, 19532, 19533, 19534,
> 19535, 19536, 19537, 19538, 19539, 19540, 19541, 19542, 19543, 19544,
> 19545, 19546, 19547, 19548, 19549, 19550, 19551, 19552, 19553, 19554,
> 19555, 19556, 19557, 19558, 19559, 19560, 19561, 19562, 19563, 19564,
> 19565, 19566, 19567, 19568, 19569, 19570, 19571, 19572, 19573, 19574,
> 19575, 19576, 19577, 19578, 19579, 19580, 19581, 19582, 19583, 19584,
> 19585, 19586, 19587, 19588, 19589, 19590, 19591, 19592, 19593, 19594,
> 19595, 19596, 19597, 19598, 19599, 19600, 19601, 19602, 19603, 19604,
> 19605, 19606, 19607, 19608, 19609, 19610, 19611, 19612, 19613, 19614,
> 19615, 19616, 19617, 19618, 19619, 19620, 19621, 19622, 19623, 19624,
> 19625, 19626, 19627, 19628, 19629, 19630, 19631, 19632, 19633, 19634,
> 19635, 19636, 19637, 19638, 19639, 19640, 19641, 19642, 19643, 19644,
> 19645, 19646, 19647, 19648, 19649, 19650, 19651, 19652, 19653, 19654,
> 19655, 19656, 19657, 19658, 19659, 19660, 19661, 19662, 19663, 19664,
> 19665, 19666, 19667, 19668, 19669, 19670, 19671, 19672, 19673, 19674,
> 19675, 19676, 19677, 19678, 19679, 19680, 19681, 19682, 19683, 19684,
> 19685, 19686, 19687, 19688, 19689, 19690, 19691, 19692, 19693, 19694,
> 19695, 19696, 19697, 19698, 19699, 19700, 19701, 19702, 19703, 19704,
> 19705, 19706, 19707, 19708, 19709 ;
> }
> I am able to open the file with GrADS by using the .ddf file:
>
> DSET ^precip.KNMI-2003.ENS50.RT3.nc
> XDEF rlon
> YDEF rlat
> VARS 3
> precip 1 -999 Total Precipitative Flux(kg m-2 s-1)
> lat=>lati 0 -999 real latitude
> lon=>longi 0 -999 real longitude
> ENDVARS
>
> With this .ddf I am able to open the netcdf file, but the precipitation is
> plotting as a function of rlon and rlat and not as a function for the real
> longitude/latitude. In other words, the data is plotting for the area west
> Africa and the data is mentioned for Europe. My GrADS version is v1.8SL11
> 32-bit big-endian on a Solaris platform.
> Does anybody know how to deal with this kind of netcdf file?
>
> Kind Regards,
> Berny
>
>
--
Sergey Varlamov
JAMSTEC, Yokohama, JAPAN
E-mail: vsm at jamstec.go.jp
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