problem display contents in hdf file

brian vant-hull brianvanthull at YAHOO.COM
Sat Jan 12 15:34:23 EST 2008 

Oh - it worked on one machine and not another!  You
didn't mention that before.  HDF is supposed to be
machine independent, so it sounds like a GrADS
portability problem.  No help from me, I hope someone
else can!

I think you are correct that the 'add_off' warning is
not fatal, but you'll still want to get it right.
Most cases it's zero, but if not your data will  be
incorrect.  It's included among the variable
attributes.

--- li zhao <janelizhao at YAHOO.COM> wrote:

> Hi Brian,
>
> I think the problem is not with scale_factor and
> add_off. Also, I did  "ncdump" on that hdf file and
> figured out the variables and included them in the
> ctl
> file when I posted my question in the previous mail.
>
> Infact I ran this script on GrADS v1.9b4 on alpha
> machine. However when I run the same version of
> grads
> on LINUX X86_64, the script gives error messages as
> I
> mentioned in the last mail.
>
>
> For your information I am attaching the errors
> again:
>  ga-> d lst_day_cmg
> HDF-SDS Read Error for dtype UINT16
> Data Request Error:  Error for variable
> 'lst_day_cmg'
> Error ocurred at column 1
> DISPLAY error:  Invalid expression
> Expression = lst_day_cmg
>
>
> Please also see the attached ctl file:
>
>
>  ***********************************************
>  dset ^MOD11C3.A2000061.004.2004116185101.hdf
>  dtype hdfsds
>  options yrev
>  undef 0s
>  unpack scale_factor add_off
>  xdef 7200 linear -180.0 0.05
>  ydef 3600 linear  -90.0 0.05
>  zdef 1 levels 1
>  tdef 1 linear 1jan1989 1dy
>  vars 16
>  LST_Day_CMG=>lst_day_cmg 1 z,y,x Monthly daytime
>  3min
>  CMG Land-surface Temperature
>  QC_Day=>qc_day 0 y,x Sea surface temperature
>  Day_view_time=>day_view_time 0 y,x Sea surface
>  temperature
>  Day_view_angl=>day_view_angl 0 y,x Sea surface
>  temperature
>  Clear_sky_days=>clear_sky_days 0 y,x Sea surface
>  temperature
>  LST_Night_CMG=>lst_night_cmg 0 y,x Sea surface
>  temperature
>  QC_Night=>qc_night 0 y,x Sea surface temperature
>  Night_view_time=>night_view_time 0 y,x Sea surface
>  temperature
>  Night_view_angl=>night_view_angl 0 y,x Sea surface
>  temperature
>  Clear_sky_Night=>clear_sky_night 0 y,x Sea surface
>  temperature
>  Emis_20=>emis_20 0 y,x Sea surface temperature
>  Emis_22=>emis_22 0 y,x Sea surface temperature
>  Emis_23=>emis_23 0 y,x Sea surface temperature
>  Emis_29=>emis_29 0 y,x Sea surface temperature
>  Emis_31=>emis_31 0 y,x Sea surface temperature
>  Emis_32=>emis_32 0 y,x Sea surface temperature
>  endvars
>
***********************************************************************
>
> regards
> Zhao
>
> --- brian vant-hull <brianvanthull at YAHOO.COM> wrote:
>
> > Zhao;
> > 'scale_factor' and 'add_off' are just example
> > variables in user's guide.  You have to provide
> > names
> > that are spelled exactly as they appear in the hdf
> > file.  Unfortunately these names often change
> > depending on the variable within each file!  In
> that
> > case you'd have to open the file separately for
> each
> > variable.
> >
> > I don't know if there's a way to have GrADS dump
> the
> > variable names so you can put them in the ctl
> file.
> > If not, IDL and Matlab have built in functions,
> and
> > you can download libraries to read hdf in C or
> > Fortran.  Or just ask someone else who's figured
> out
> > how to use your particular dataset.  Once you have
> > the
> > correct names for the offset and scale you are
> good
> > to
> > go.
> >
> > Anybody who has worked with hdf before should be
> > able
> > to give you something that will get the variable
> > names
> > for you, but it's a multiple step process or
> > program.
> > If you have IDL or Matlab go to
> > http://www.atmos.umd.edu/~gcm and click on the
> blue
> > useful button, then go down to the link about
> > reading
> > hdf in matlab and IDL.  This will show you how to
> go
> > about it.
> >
> > -Brian.
> >
> > --- li zhao <janelizhao at YAHOO.COM> wrote:
> >
> > > Hi everybody,
> > >
> > > Probably this is a simple fix but I must be
> > missing
> > > something. I try to open a hdf file and it loads
> > > well,
> > > but giving the following error message when
> > > displaying
> > > the variable.
> > >
> > > ga-> d lst_day_cmg
> > > Warning: HDF attribute named "add_off" does not
> > > exist
> > > Warning: Could not retrieve "add_off" -- setting
> > to
> > > 0.0
> > > HDF-SDS Read Error for dtype UINT16
> > > Data Request Error:  Error for variable
> > > 'lst_day_cmg'
> > >   Error ocurred at column 1
> > > DISPLAY error:  Invalid expression
> > >   Expression = lst_day_cmg
> > >
> > >
> > > Grads configuration as follows:
> > > (Config: v1.9b4 32-bit little-endian readline
> > > sdf/xdf
> > > hdf-sds netcdf lats printim)
> > >
> > >
> > > Below is the actual ctl file I am using:
> > >
> > > ***********************************************
> > > dset ^MOD11C3.A2000061.004.2004116185101.hdf
> > > dtype hdfsds
> > > options yrev
> > > undef 0s
> > > unpack scale_factor add_off
> > > xdef 7200 linear -180.0 0.05
> > > ydef 3600 linear  -90.0 0.05
> > > zdef 1 levels 1
> > > tdef 1 linear 1jan1989 1dy
> > > vars 16
> > > LST_Day_CMG=>lst_day_cmg 1 z,y,x Monthly daytime
> > > 3min
> > > CMG Land-surface Temperature
> > > QC_Day=>qc_day 0 y,x Sea surface temperature
> > > Day_view_time=>day_view_time 0 y,x Sea surface
> > > temperature
> > > Day_view_angl=>day_view_angl 0 y,x Sea surface
> > > temperature
> > > Clear_sky_days=>clear_sky_days 0 y,x Sea surface
> > > temperature
> > > LST_Night_CMG=>lst_night_cmg 0 y,x Sea surface
> > > temperature
> > > QC_Night=>qc_night 0 y,x Sea surface temperature
> > > Night_view_time=>night_view_time 0 y,x Sea
> surface
> > > temperature
> > > Night_view_angl=>night_view_angl 0 y,x Sea
> surface
> > > temperature
> > > Clear_sky_Night=>clear_sky_night 0 y,x Sea
> surface
> > > temperature
> > > Emis_20=>emis_20 0 y,x Sea surface temperature
> > > Emis_22=>emis_22 0 y,x Sea surface temperature
> > > Emis_23=>emis_23 0 y,x Sea surface temperature
> > > Emis_29=>emis_29 0 y,x Sea surface temperature
> > > Emis_31=>emis_31 0 y,x Sea surface temperature
> > > Emis_32=>emis_32 0 y,x Sea surface temperature
> > > endvars
> > >
> > > Thanks for your help,
> > > Zhao
> > >
> > >
> > >
> > >
> >
>
=== message truncated ===


Brian Vant-Hull
917-318-4481


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