EMPTY plots when entire domain values = ZERO

[Davide Sacchetti]

grads cannot create contours of a constant field (eg.: all values =0)

I know only two solutions:
1) test by set gxout stat if the field is constant or not, then decide
what to plot
2) if contour levels have been fixed (eg 'set clevs 1 5 10 ...') you
could add a minimal noise to your field (eg: 'd cc+lon/10000000)

hoping this is the answer you were looking for
bye bye
Davide

On Wed, 2007-09-12 at 15:26 -0700, Kevin M Levey wrote:
> WED 12SEP07: 1525PDT
>
> Hi All.
>
> I've come across a problem that I am a little stumped on and it's the first
> time I've encountered this error.
>
> I am plotting GFS (1x1 degree) convective cloud values and if I plot the
> entire dataset, the plot comes out fine with convective cloud showing up.
> However, if I choose a smaller domain where ALL grid points are 0, I expect
> GRADS to plot the zero value, however, instead I get a blank plot. Has
> anyone ever come across this problem before?
>
> Running GRADSC from the command line gives me the following output:
>
> ga-> test
> No hardcopy metafile open
> All files closed; all defined objects released
> All GrADS attributes have been reinitialized
> Cannot plot color bar: No shading information
>
>
> If I make the domain larger where there is at least one grid box with a
> value > 0 then the plot comes out OK.
>
> A copy of the test script:
>
> 'reinit'
> 'set mpdset hires'
> 'set mpt * off'
> 'set mpt 0 0 1 6'
> 'set mpt 1 0 1 1'
> 'set grads off'
> 'set timelab on'
> 'set display color white'
> 'clear'
> 'open /prod/custom/Input/modelplots/GFS/temp/gfs_102.ctl'
> 'clear'
> 'set xsize 800 600'
> 'set display color white'
> 'set lat -36 -16'
> 'set lon 10 36'
> 'set map auto 1 1 6'
> 'define cc = TCDCcvl'
>
> 'run /prod/custom/Input/modelplots/GFS/scripts/rgbset_cloud2.gs'
> 'set gxout shaded'
> 'set csmooth on'
> 'd cc'
>
> 'run /prod/custom/Input/modelplots/GFS/scripts/SA_cities_clouds.gs'
> 'run /prod/custom/Input/modelplots/GFS/scripts/cbarn'
> 'draw title  CONVECTIVE CLOUD COVER (%) \INIT: 12UTC 12SEP07
> VALID: 20H00 SUN 16 SEP 2007'
>
> The above domain for this hour has ALL grid points over South Africa = ZERO,
> but grads wont plot anything. The forecast hour before and after where at
> least one gridpoint has a value  > 0 then the plots came out just fine, and
> it only happens when ALL grid points for the domain are ZERO.
>
> Any help would be appreciated indeed.
>
> Thanks.
>
> GRADS information:
>
> Built Mon May 23 13:17:11 EDT 2005 for i686-pc-linux-gnu
>
> This version of GrADS has been configured with the following options:
>
>    o This is a 32-bit LITTLE ENDIAN machine version.
>    o Command line editing (readline) ENABLED.
>    o CIRES/CDC (http://www.cdc.noaa.gov) SDF/XDF interface DISABLED.
>      This version is NOT configured to read NetCDF/HDF-SDS files.
>    o DTYPE netcdf and DTYPE hdfsds are DISABLED.
>    o OPeNDAP (a.k.a. DODS) gridded data interface DISABLED.
>    o OPeNDAP (a.k.a. DODS) station data interface DISABLED.
>    o PCMDI (http://www-pcmdi.llnl.gov) LATS interface ENABLED.
>      This version is configured to write GRIB files (but no NetCDF/HDF
> files).
>    o DAO (http://dao.gsfc.nasa.gov) Athena Widget GUI DISABLED.
>    o NRL/DAO/PCMDI XA or ImageMagick Image Output DISABLED.
>    o printim command for direct png/gif output ENABLED.
>      (via the GD Library -- http://www.boutell.com/gd)
>
> Regards
>
> Kevin M Levey, MSc (University of Cape Town)
> Director of Meteorological Operations
> CustomWeather, Inc
> San Francisco, CA, USA
>
> http://www.1stweather.com
> http://www.myforecast.com
> http://www.customweather.com
>
--
Sacchetti Davide
ARPAL UO3 Centro Meteo Idrologico Regione Liguria - Dir. Scientifica
V.le Brigare Partigiane 2 16121 Genova (I)
tel: +39 010 6437535
mail: davide.sacchetti at arpal.org   web: www.meteoliguria.it