[ncl-talk] how to read a variable in group of hdf file?

[David Brown]

There are certain variables, specifically coordinate variables, that are
alluded to in the metadata when the file is read as HDF, but which are not
visible as variables. To actually get the coordinate values you need to
read the file as HDFEOS. The HDFEOS reader has specialized support for
HDFEOS coordinates. From your print out, it appears that there are 3
different swaths in the files (in HDF terms these are represented as
different groups), and 3 corresponding coordinates named 'Time'. Since I
think this is an HDFEOS2 file, NCL appends the group name to variables
within the group. So for example Time_Low_Res_Swath means the Time
coordinate variable in the Low_Res_Swath group.
The HDFEOS2 reader was written before support for groups was added to NCL,
so you cannot use the group syntax. However, all the variables in the
HDFEOS file should be available. Hope this helps.
 -dave



On Tue, Nov 4, 2014 at 10:13 AM, dyjbean at gmail.com <dyjbean at gmail.com>
wrote:

>
> after i have changed the suffix of AMSR_E_L2A_201108010017_D.hdf into AMSR_E_L2A_201108010017_D.hdf.hdfeos,
> there gave a
> another variation, the "Time" variable has new variable names:
>
> double Time_High_Res_B_Swath ( DataTrack_lo_High_Res_B_Swath )
> double Time_High_Res_A_Swath ( DataTrack_lo_High_Res_A_Swath )
> double Time_Low_Res_Swath ( DataTrack_lo_Low_Res_Swath )
>
> above these three variables didn't appear in hdf file but in hdfeos,this
> is a file format change.
>
>
>
> ------------------------------
>  dyjbean at gmail.com
>
>
> *From:* 李嘉鹏 <lijpbasin at 126.com>
> *Date:* 2014-11-04 18:32
> *To:* ncl-talk <ncl-talk at ucar.edu>
> *Subject:* Re: [ncl-talk] how to read a variable in group of hdf file?
> Hi, Try `ncl_filedump AMSR_E_L2A_201108010017_D.hdf`, it might give you
> some hints of the corresponding variable name in NCL.
>
> On November 4, 2014 6:13:49 PM GMT+08:00, "dyjbean at gmail.com" <
> dyjbean at gmail.com> wrote:
> >hi,
> >i want to read a variable "Time" which is involved in group  in a hdf
> >file, a part of information of this hdf file is as follows:
> >+++++++++++++++++++++++++++++++++++++++++++
> >......
> >GROUP=GeoField
> >OBJECT=GeoField_1
> >GeoFieldName="Time"
> >DataType=DFNT_FLOAT64
> >DimList=("DataTrack_lo")
> >END_OBJECT=GeoField_1
> >OBJECT=GeoField_2
> >GeoFieldName="Latitude"
> >DataType=DFNT_FLOAT32
> >DimList=("DataTrack_lo","DataXTrack_lo")
> >END_OBJECT=GeoField_2
> >OBJECT=GeoField_3
> >GeoFieldName="Longitude"
> >DataType=DFNT_FLOAT32
> >DimList=("DataTrack_lo","DataXTrack_lo")
> >END_OBJECT=GeoField_3
> >END_GROUP=GeoField
> >......
> >++++++++++++++++++++++++++++++++++++++++++++++++++
> >
> >i want to extract the "Time" in ncl, but it showed:
> >+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
> >
> >ncl 0> ff=addfile("AMSR_E_L2A_201108010017_D.hdf","r")
> >ncl 1> time=ff->Time
> >fatal:["Execute.c":6321]:variable (Time) is not in file (ff)
> >fatal:["Execute.c":8565]:Execute: Error occurred at or near line 1
> >+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
> >
> >it seems that there doesn't exist "Time" variable in this hdf file,but
> >it does,
> >
> >how can i read this time info in ncl?
> >
> >
> >thanks
> >
> >
> >
> >
> >dyjbean at gmail.com
> >
> >
> >------------------------------------------------------------------------
> >
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