How to use the nansat.tools.gdal.Open function in nansat

metaDict = []
        bandDatasetMask = 'HDF4_EOS:EOS_SWATH:"%s":%s:ImageData'
        for bandName, bandWave in zip(bandNames, bandWaves):
            metaEntry = {'src': {'SourceFilename': (bandDatasetMask
                                                    % (filename, bandName)),
                                 'SourceBand': 1,
                                 'DataType': 6,
                                 },
                         'dst': {'wkv': 'toa_outgoing_spectral_radiance',
                                 'wavelength': str(bandWave),
                                 'suffix': str(bandWave),
                                 }}
            metaDict.append(metaEntry)

        # create empty VRT dataset with geolocation only
        gdalSubDataset = gdal.Open(metaDict[0]['src']['SourceFilename'])
        self._init_from_gdal_dataset(gdalSubDataset, metadata=gdalSubDataset.GetMetadata())

        # add bands with metadata and corresponding values to the empty VRT
        self.create_bands(metaDict)

        # find largest lon/lat subdatasets
        latShape0 = 0
        for subDataset in subDatasets:
            if 'Latitude' in subDataset[1]:
                ls = int(subDataset[1].strip().split('[')[1].split('x')[0])
                if ls >= latShape0:
                    latShape0 = ls
                    latSubDS = subDataset[0]
            if 'Longitude' in subDataset[1]:
                ls = int(subDataset[1].strip().split('[')[1].split('x')[0])
                if ls >= latShape0:

-----------
        fileName : string
        gdalDataset : gdal dataset
        gdalMetadata : gdal metadata
        latlonGrid : numpy 2 layered 2D array with lat/lons of desired grid
        '''
        # test if input files is ASCAT
        iDir, iFile = os.path.split(fileName)
        iFileName, iFileExt = os.path.splitext(iFile)
        try:
            assert iFileName[0:6] == 'ascat_' and iFileExt == '.nc'
        except:
            raise WrongMapperError

        # Create geolocation
        subDataset = gdal.Open('NETCDF:"' + fileName + '":lat')
        self.GeolocVRT = VRT(srcRasterXSize=subDataset.RasterXSize,
                             srcRasterYSize=subDataset.RasterYSize)

        GeolocMetaDict = [{'src': {'SourceFilename': ('NETCDF:"' + fileName +
                                                      '":lon'),
                                   'SourceBand': 1,
                                   'ScaleRatio': 0.00001,
                                   'ScaleOffset': -360},
                           'dst': {}},
                          {'src': {'SourceFilename': ('NETCDF:"' + fileName +
                                                      '":lat'),
                                   'SourceBand': 1,
                                   'ScaleRatio': 0.00001,
                                   'ScaleOffset': 0},
                           'dst': {}}]

simFilesMask = os.path.join(iDir, iFileName[0:30] + '*.nc')
        simFiles = glob.glob(simFilesMask)
        print('simFilesMask, simFiles', simFilesMask, simFiles)

        metaDict = []
        for simFile in simFiles:
            print('simFile', simFile)
            # open file, get metadata and get parameter name
            simSupDataset = gdal.Open(simFile)
            simSubDatasets = simSupDataset.GetSubDatasets()
            simWKV = None
            for simSubDataset in simSubDatasets:
                if '_mean' in simSubDataset[0]:
                    simValidSupDataset = simSupDataset
                    simGdalDataset = gdal.Open(simSubDataset[0])
                    simBand = simGdalDataset.GetRasterBand(1)
                    simBandMetadata = simBand.GetMetadata()
                    simVarname = simBandMetadata['NETCDF_VARNAME']
                    # get WKV
                    print('    simVarname', simVarname)
                    if simVarname in self.varname2wkv:
                        simWKV = self.varname2wkv[simVarname]
                        break

            # skipp adding this similar file if it is not valid
            if simWKV is None:
                continue

            metaEntry = {
                'src': {'SourceFilename': simSubDataset[0],
                        'SourceBand':  1},

else:
            antennaPointing = -90
        rs2_3 = rs2_1.node('orbitAndAttitude').node('orbitInformation')
        passDirection = rs2_3['passDirection']

        # create empty VRT dataset with geolocation only
        VRT.__init__(self, gdalDataset)

        #define dictionary of metadata and band specific parameters
        pol = []
        metaDict = []

        # Get the subdataset with calibrated sigma0 only
        for dataset in gdalDataset.GetSubDatasets():
            if dataset[1] == 'Sigma Nought calibrated':
                s0dataset = gdal.Open(dataset[0])
                s0datasetName = dataset[0][:]
                band = s0dataset.GetRasterBand(1)
                s0datasetPol = band.GetMetadata()['POLARIMETRIC_INTERP']
                for i in range(1, s0dataset.RasterCount+1):
                    iBand = s0dataset.GetRasterBand(i)
                    polString = iBand.GetMetadata()['POLARIMETRIC_INTERP']
                    suffix = polString
                    # The nansat data will be complex
                    # if the SAR data is of type 10
                    dtype = iBand.DataType
                    if dtype == 10:
                        # add intensity band
                        metaDict.append(
                            {'src': {'SourceFilename':
                                     ('RADARSAT_2_CALIB:SIGMA0:'
                                      + fileName + '/product.xml'),

# Get file names from dataset or subdataset
        subDatasets = gdalDataset.GetSubDatasets()
        if len(subDatasets) == 0:
            fileNames = [fileName]
        else:
            fileNames = [f[0] for f in subDatasets]

        # add bands with metadata and corresponding values to the empty VRT
        metaDict = []
        geoFileDict = {}
        xDatasetSource = ''
        yDatasetSource = ''
        firstXSize = 0
        firstYSize = 0
        for i, fileName in enumerate(fileNames):
            subDataset = gdal.Open(fileName)
            # choose the first dataset whith grid
            if (firstXSize == 0 and firstYSize == 0 and
                    subDataset.RasterXSize > 1 and subDataset.RasterYSize > 1):
                firstXSize = subDataset.RasterXSize
                firstYSize = subDataset.RasterYSize
                firstSubDataset = subDataset
                # get projection from the first subDataset
                projection = firstSubDataset.GetProjection()

            # take bands whose sizes are same as the first band.
            if (subDataset.RasterXSize == firstXSize and
                    subDataset.RasterYSize == firstYSize):
                if projection == '':
                    projection = subDataset.GetProjection()
                if ('GEOLOCATION_X_DATASET' in fileName or
                        'longitude' in fileName):

self.correct_geolocation_data()

        # read manifest file
        manifest_data = self.read_manifest_data(manifest_files[0])

        # very fast constructor without any bands only with some metadata and geolocation
        self._init_empty(manifest_data, self.annotation_data)

        # skip adding bands in the fast mode and RETURN
        if fast:
            return

        # Open data files with GDAL
        gdalDatasets = {}
        for pol in polarizations:
            gdalDatasets[pol] = gdal.Open(mds_files[pol])

            if not gdalDatasets[pol]:
                raise WrongMapperError('%s: No Sentinel-1 datasets found' % mds_files[pol])

        # Check metadata to confirm it is Sentinel-1 L1
        metadata = gdalDatasets[polarizations[0]].GetMetadata()

        # create full size VRTs with incidenceAngle and elevationAngle
        annotation_vrts = self.vrts_from_arrays(self.annotation_data,
                                                ['incidenceAngle', 'elevationAngle'])
        self.band_vrts.update(annotation_vrts)

        # create full size VRTS with calibration LUT
        calibration_names = ['sigmaNought', 'betaNought']
        calibration_list_tag = 'calibrationVectorList'
        for calibration_file in calibration_files:

Number_lines = int(gdalMetadata['NC_GLOBAL#Number_lines'])
            Number_columns = int(gdalMetadata['NC_GLOBAL#Number_columns'])
            Element_x_size = float(gdalMetadata['NC_GLOBAL#Element_x_size'])
            Element_y_size = float(gdalMetadata['NC_GLOBAL#Element_y_size'])
        except:
            raise WrongMapperError

        # find subdataset with DEPTH
        subDatasets = gdalDataset.GetSubDatasets()
        dSourceFile = None
        for subDataset in subDatasets:
            if subDataset[0].endswith('.mnt":DEPTH'):
                dSourceFile = subDataset[0]
        if dSourceFile is None:
            raise WrongMapperError
        dSubDataset = gdal.Open(dSourceFile)
        dMetadata = dSubDataset.GetMetadata()

        try:
            scale_factor = dMetadata['DEPTH#scale_factor']
            add_offset = dMetadata['DEPTH#add_offset']
        except:
            raise WrongMapperError

        geoTransform = [mbWestLongitude, Element_x_size, 0,
                        mbNorthLatitude, 0, -Element_y_size]

        # create empty VRT dataset with geolocation only
        VRT.__init__(self, srcGeoTransform=geoTransform,
                           srcMetadata=gdalMetadata,
                           srcProjection=NSR(mbProj4String).wkt,
                           srcRasterXSize=Number_columns,

test_openable(self.fileName)
        else:
            ff = glob.glob(os.path.join(self.fileName,'*.*'))
            for f in ff:
                test_openable(f)
        # lazy import of nansat mappers
        # if nansat mappers were not imported yet
        global nansatMappers
        if nansatMappers is None:
            nansatMappers = _import_mappers()

        # open GDAL dataset. It will be parsed to all mappers for testing
        gdalDataset = None
        if self.fileName[:4] != 'http':
            try:
                gdalDataset = gdal.Open(self.fileName)
            except RuntimeError:
                self.logger.error('GDAL could not open ' + self.fileName +
                                  ', trying to read with Nansat mappers...')
        if gdalDataset is not None:
            # get metadata from the GDAL dataset
            metadata = gdalDataset.GetMetadata()
        else:
            metadata = None

        tmpVRT = None

        importErrors = []
        if mapperName is not '':
            # If a specific mapper is requested, we test only this one.
            # get the module name
            mapperName = 'mapper_' + mapperName.replace('mapper_',

# Get file names from dataset or subdataset
        subDatasets = gdalDataset.GetSubDatasets()
        if len(subDatasets) == 0:
            filenames = [inputFileName]
        else:
            filenames = [f[0] for f in subDatasets]

        # add bands with metadata and corresponding values to the empty VRT
        metaDict = []
        xDatasetSource = ''
        yDatasetSource = ''
        firstXSize = 0
        firstYSize = 0
        for _, filename in enumerate(filenames):
            subDataset = gdal.Open(filename)
            # choose the first dataset whith grid
            if (firstXSize == 0 and firstYSize == 0 and
                    subDataset.RasterXSize > 1 and subDataset.RasterYSize > 1):
                firstXSize = subDataset.RasterXSize
                firstYSize = subDataset.RasterYSize
                firstSubDataset = subDataset
                # get projection from the first subDataset
                projection = firstSubDataset.GetProjection()

            # take bands whose sizes are same as the first band.
            if (subDataset.RasterXSize == firstXSize and
                    subDataset.RasterYSize == firstYSize):
                if projection == '':
                    projection = subDataset.GetProjection()
                if ('GEOLOCATION_X_DATASET' in filename or
                        'longitude' in filename):