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{scrollbar} h2. |
Exercise
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outline
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We
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want
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to
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download
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a
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NetCdf
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file
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from
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the
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opendap
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server
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(
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),
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and
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read
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the
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variables,
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dimensions
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and
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data.
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Download
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a
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NetCdf
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file
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and
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read
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its
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data
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Add
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the
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following
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import
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statements
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to
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the
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region
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Import
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libs
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:
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} # python libs import urllib from FmWorkshopHelperFunctions import * # DeltaShell libs from DelftTools.Utils.NetCdf import NetCdfFile {code} |
These
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will
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add
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the
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libraries
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"urllib"
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(python
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lib
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containing
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the
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code
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to
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download
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urls),
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FmWorkshopHelperFunctions
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(python
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lib
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containing
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helper
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functions
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for
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working
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with
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arrays)
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and
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NetCdfFile
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(DeltaShell
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code
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for
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working
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with
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NetCdf
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files).
And add this code to the end of the script :
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\\ And add this code to the end of the script : {code:language=python} #region Read NetCdf file # Download file from opendap remote_path = "http://opendap.deltares.nl/static/deltares/delftdashboard/toolboxes/TideStations/iho.nc" urllib.urlretrieve (remote_path, rootPath + "iho.nc") file = NetCdfFile.OpenExisting(rootPath + "iho.nc") # Show all variables for var in file.GetVariables(): print file.GetVariableName(var) # Show all dimensions for dim in file.GetAllDimensions(): print file.GetDimensionName(dim) # Get variables stations = file.GetVariableByName("stations") components = file.GetVariableByName("components") # Get dimensions nrOfStations = file.GetDimensionLength(file.GetDimension("stations")) nrOfComponents = file.GetDimensionLength(file.GetDimension("components")) componentNameLength = file.GetDimensionLength(file.GetDimension("component_string_length")) stationNameLength = file.GetDimensionLength(file.GetDimension("name_string_length")) # Get data stationNames = Transpose2DCharArrayToStringList(file.Read(stations),stationNameLength, nrOfStations) componentNames = Transpose2DCharArrayToStringList(file.Read(components),componentNameLength, nrOfComponents) latData = file.Read(file.GetVariableByName("lat")) lonData = file.Read(file.GetVariableByName("lon")) phaseData = file.Read(file.GetVariableByName("amplitude")) amplitudeData = file.Read(file.GetVariableByName("amplitude")) #endregion {code} \\ The first statements will copy the |
The first statements will copy the iho.nc
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file
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to
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a
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local
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directory
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(in
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our
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case
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rootPath)
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} # Download file from opendap remote_path = "http://opendap.deltares.nl/static/deltares/delftdashboard/toolboxes/TideStations/iho.nc" urllib.urlretrieve (remote_path, rootPath + "iho.nc") {code} \\ Then we continue by reading the file using the DeltaShell NetCdfFile class and showing all the variable and dimension names in the message window of DeltaShell by using the print statement {code:language=python} |
Then we continue by reading the file using the DeltaShell NetCdfFile class and showing all the variable and dimension names in the message window of DeltaShell by using the print statement
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file = NetCdfFile.OpenExisting(rootPath + "iho.nc") # Show all variables for var in file.GetVariables(): print file.GetVariableName(var) # Show all dimensions for dim in file.GetAllDimensions(): print file.GetDimensionName(dim) |
Now that we know what the names of the dimensions and variables are we can use them to retrieve them with this code:
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{code}
\\
Now that we know what the names of the dimensions and variables are we can use them to retrieve them with this code:
{code:language=python}
# Get variables
stations = file.GetVariableByName("stations")
components = file.GetVariableByName("components")
# Get dimensions
nrOfStations = file.GetDimensionLength(file.GetDimension("stations"))
nrOfComponents = file.GetDimensionLength(file.GetDimension("components"))
componentNameLength = file.GetDimensionLength(file.GetDimension("component_string_length"))
stationNameLength = file.GetDimensionLength(file.GetDimension("name_string_length"))
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And retrieve the data for the variables :
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{code} \\ And retrieve the data for the variables : {code:language=python} # Get data stationNames = Transpose2DCharArrayToStringList(file.Read(stations),stationNameLength, nrOfStations) componentNames = Transpose2DCharArrayToStringList(file.Read(components),componentNameLength, nrOfComponents) latData = file.Read(file.GetVariableByName("lat")) lonData = file.Read(file.GetVariableByName("lon")) phaseData = file.Read(file.GetVariableByName("amplitude")) amplitudeData = file.Read(file.GetVariableByName("amplitude")) {code} \\ \\ |
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