[R-sig-Geo] get data from nc file

[Antonio Silva]

Dear list members

I downloaded some nc files with precipitation data from
https://pmm.nasa.gov/data-access/downloads/trmm (Level 3 3B43:
Multisatellite Precipitation). For the image link see the global attribute
"history" (below).

With ncdf4::nc_open I cloud open the file (nc.data <- nc_open("
3B43.20080101.7A.HDF.nc")

I want to extract the "StartGranuleDateTime" but it is inside the global
attribute FileHeader (see below).

With ncatt_get(nc.data,0,"FileHeader")$value I got
[1]
"AlgorithmID=3B43;\nAlgorithmVersion=3B43_7.0;\nFileName=3B43.20080101.7A.HDF;\nGenerationDateTime=2012-11-29T19:12:01.000Z;\nStartGranuleDateTime=2008-01-01T00:00:00.000Z;\nStopGranuleDateTime=2008-01-31T23:59:59.999Z;\nGranuleNumber=;\nNumberOfSwaths=0;\nNumberOfGrids=1;\nGranuleStart=;\nTimeInterval=MONTH;\nProcessingSystem=PPS;\nProductVersion=7A;\nMissingData=;\n"

Is there any way to extract only the string "2008-01-01T00:00:00.000Z"?

The best I could do was
as.Date(substr(strsplit(ncatt_get(nc.data,0,"FileHeader")$value,";\n")[[1]][5],22,45),"%Y-%m-%dT%H:%M:%OSZ")

but probably, I suppose, there must be a more direct way of getting the
data. I appreciate any suggestions.

Best regards,

Antonio Olinto
Fisheries Institute
Brazil

nc.data
File 3B43.20080101.7A.HDF.nc (NC_FORMAT_CLASSIC):

     1 variables (excluding dimension variables):
        float precipitation[nlat,nlon]
            units: mm/hr
            coordinates: nlon nlat
            _FillValue: -9999.900390625

     2 dimensions:
        nlon  Size:33
            long_name: longitude
            standard_name: longitude
            units: degrees_east
        nlat  Size:41
            long_name: latitude
            standard_name: latitude
            units: degrees_north

    5 global attributes:
        Grid.GridHeader: BinMethod=ARITHMETIC_MEAN;
Registration=CENTER;
LatitudeResolution=0.25;
LongitudeResolution=0.25;
NorthBoundingCoordinate=50;
SouthBoundingCoordinate=-50;
EastBoundingCoordinate=180;
WestBoundingCoordinate=-180;
Origin=SOUTHWEST;

        FileHeader: AlgorithmID=3B43;
AlgorithmVersion=3B43_7.0;
FileName=3B43.20080101.7A.HDF;
GenerationDateTime=2012-11-29T19:12:01.000Z;
StartGranuleDateTime=2008-01-01T00:00:00.000Z;
StopGranuleDateTime=2008-01-31T23:59:59.999Z;
GranuleNumber=;
NumberOfSwaths=0;
NumberOfGrids=1;
GranuleStart=;
TimeInterval=MONTH;
ProcessingSystem=PPS;
ProductVersion=7A;
MissingData=;

        FileInfo: DataFormatVersion=m;
TKCodeBuildVersion=1;
MetadataVersion=m;
FormatPackage=HDF Version 4.2 Release 4, January 25, 2009;
BlueprintFilename=TRMM.V7.3B43.blueprint.xml;
BlueprintVersion=BV_13;
TKIOVersion=1.6;
MetadataStyle=PVL;
EndianType=LITTLE_ENDIAN;

        GridHeader: BinMethod=ARITHMETIC_MEAN;
Registration=CENTER;
LatitudeResolution=0.25;
LongitudeResolution=0.25;
NorthBoundingCoordinate=50;
SouthBoundingCoordinate=-50;
EastBoundingCoordinate=180;
WestBoundingCoordinate=-180;
Origin=SOUTHWEST;

        history: 2018-12-26 17:57:56 GMT Hyrax-1.13.4
https://disc2.gesdisc.eosdis.nasa.gov:443/opendap/TRMM_L3/TRMM_3B43.7/2008/3B43.20080101.7A.HDF.nc?precipitation[604:636][3:43],nlat[3:43],nlon[604:636]

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