;
;  This example code illustrates how to access and visualize LaRC
;  CERES ES8 NOAA20 HDF4 Grid file in IDL.
;
; If you have any questions, suggestions, comments  on this example, 
; please use the HDF-EOS Forum (http://hdfeos.org/forums).
;
;  If you would like to see an  example of any other NASA HDF/HDF-EOS 
; data product that is not listed in the HDF-EOS Comprehensive Examples page
; (http://hdfeos.org/zoo), feel free to contact us at eoshelp@hdfgroup.org
; or post it at the HDF-EOS Forum (http://hdfeos.org/forums).
;
; Usage:
;
;  $idl CER_ES8_NOAA20-FM6_Edition1_101109.20220201.hdf.idl
;
; Tested under: IDL 8.8.3
; Last updated: 2022-12-01

; Open file.
file_name='CER_ES8_NOAA20-FM6_Edition1_101109.20220201.hdf'
file_id_hdf=HDF_SD_START(file_name, /READ)

; Read data.
datafield_name='CERES LW flux at TOA'
index = HDF_SD_NAMETOINDEX(file_id_hdf, datafield_name)
sds_id=HDF_SD_SELECT(file_id_hdf, index)
HDF_SD_GETDATA, sds_id, data

fillvalue_index=HDF_SD_ATTRFIND(sds_id, '_FillValue')
HDF_SD_ATTRINFO, sds_id, fillvalue_index, data=fillvalue

long_name_index=HDF_SD_ATTRFIND(sds_id, 'long_name')
HDF_SD_ATTRINFO, sds_id, long_name_index, DATA=long_name

units_index=HDF_SD_ATTRFIND(sds_id, 'units')
HDF_SD_ATTRINFO, sds_id, units_index, DATA=units

HDF_SD_ENDACCESS, sds_id

; Retrieve latitude.
datafield_name='Colatitude of CERES FOV at TOA'
index = HDF_SD_NAMETOINDEX(file_id_hdf, datafield_name)
sds_id=HDF_SD_SELECT(file_id_hdf, index)

fillvalue_index=HDF_SD_ATTRFIND(sds_id, '_FillValue')
HDF_SD_ATTRINFO, sds_id, fillvalue_index, data=fv_lat

HDF_SD_GETDATA, sds_id, colat
HDF_SD_ENDACCESS, sds_id

; Retrieve longitude.
datafield_name='Longitude of CERES FOV at TOA'
index = HDF_SD_NAMETOINDEX(file_id_hdf, datafield_name)
sds_id=HDF_SD_SELECT(file_id_hdf, index)

fillvalue_index=HDF_SD_ATTRFIND(sds_id, '_FillValue')
HDF_SD_ATTRINFO, sds_id, fillvalue_index, data=fv_lon

HDF_SD_GETDATA, sds_id, lon
HDF_SD_ENDACCESS, sds_id

; Close file.
HDF_SD_END, file_id_hdf

; Convert data type.
dataf=FLOAT(data)
lon=FLOAT(lon)
colat=FLOAT(colat)

; Process fill value.
idx=WHERE(data EQ fillvalue(0), cnt)
if cnt gt 0 then dataf[idx]=!Values.F_NAN

idx = where(lon eq fv_lon(0), cnt)
if cnt gt 0 then lon[idx] = !Values.F_NAN

idx = where(colat eq fv_lat(0), cnt)
if cnt gt 0 then colat[idx] = !Values.F_NAN

lat=90-colat
lon[WHERE(FINITE(lon) GT 180)] = lon[WHERE(FINITE(lon) GT 180)] - 360

EXIT