def extractVerticalSection(nc,dataVar,vertSection,tIndex,coordVal):
""" Takes five arguments; the NetCDF dataset, the variable object, the
string reprenting verticle setion, the index along the time axis and the
index along the latitude/longitude. Using the arguments it extracts returns
the data, from a NetCDF file"""
import netcdfUtils
# Find the number of dimensions for the data variable
numDims = len(dataVar.dimensions)
# check number of dimensions and raise error if they are not 2,or 3,or 4
if numDims < 3 or numDims > 4:
raise ValueError("Cannot extract data from variable with %d dimensions" % numDims)
# Check if the longitude, latitude and vertical dimensions are present
lonVar = netcdfUtils.findLongitudeVar(nc, dataVar)
latVar = netcdfUtils.findLatitudeVar(nc, dataVar)
zVar=netcdfUtils.findVerticalVar(nc,dataVar)
#raise error if the longitude, latitude and vertical dimensions are abscent
if lonVar is None or latVar is None or zVar is None:
raise ValueError("Cannot extract map data if longitude, latitude and Vertical dimensios are abscent")
# change longitutude value from range (-180 to 180) into (0 to 360)
if vertSection=='NS':
#Map the slicing longitude from -180-to-180 to 0-360
if min(lonVar[:])>=0:
if coordVal<=0:
coordVal=coordVal+180
else:
coordVal=coordVal+180
#the dimensions present are time, vertical, latitude or longitude
if vertSection=='NS'and numDims == 4:
coordVar=netcdfUtils.findLongitudeVar(nc, dataVar)
coordIndex=utils.findNearestIndex(coordVar,coordVal)
return dataVar[tIndex,:,:,coordIndex]
# the dimensions present must be vertical, latitude or longitude
elif vertSection=='NS'and numDims == 3:
coordVar=netcdfUtils.findLongitudeVar(nc, dataVar)
coordIndex=utils.findNearestIndex(coordVar,coordVal)
return dataVar[:,:,coordIndex]
# the dimensions present are time, vertical, latitude & longitude in that order
if vertSection=='EW'and numDims == 4:
coordVar=netcdfUtils.findLatitudeVar(nc, dataVar)
coordIndex=utils.findNearestIndex(coordVar,coordVal)
return dataVar[tIndex,:,coordIndex,:]
# the dimensions present must be vertical, latitude & longitude in that order
elif vertSection=='EW'and numDims == 3:
coordVar=netcdfUtils.findLatitudeVar(nc, dataVar)
coordIndex=utils.findNearestIndex(coordVar,coordVal)
return dataVar[:,coordIndex,:]
def findNearestLonIndex(nc,dataVar,lonval):
""" Searches through longitude values for the target value, returning the index
of the longitude value that is closest numerically to the target value.
If more than one longitude value is equally close to the target, the index
of the first value will be returned. """
import utils
import netcdfUtils
# map the longitutude value from range (-180 to 180) onto (0 to 360) in the data file
coordval=netcdfUtils.findLongitudeVar(nc,dataVar)
if min(coordval[:])>=0:
#check if the latitude value is within the latitude range
if lonval<=0:
lonval=lonval+180
else:
lonval=lonval+180
# check if the Variable object representing the latitude axis exists in the netcdf file
if coordval is None:
raise ValueError("No Variable object for the longitude axis exists in the netcdf file")
#create an array of longitude values from where to search
lonvals=coordval[:]
#find the index of the given longitudevalue and check if it exists
lonIndex=utils.findNearestIndex(lonvals,lonval)
#if no index is found
if lonIndex is None:
raise ValueError("No index value found for the longitude value entered")
#longitude index value
return lonIndex
def extractTimeseries(nc,dataVar,lonVal,latVal,zVal):
""" Takes five arguments; the NetCDF dataset, the variable object, the
longitude value, the latitude value and the vertical value and use them to
extracts data and time values at the point described. It returns the data of
the and variable represented by the variable object the time values for
each point described by the longitude, latitude and vertical values in the
NetCDF file"""
# Find the number of dimensions for the data variable
numDims = len(dataVar.dimensions)
# Check if the number of dimensions and raise error if they are not 3 or 4
if numDims < 3 or numDims > 4:
raise ValueError("Cannot extract data from variable with %d dimensions" % numDims)
# Check if longitude, latitude and vertical dimensions are present
lonVar = netcdfUtils.findLongitudeVar(nc, dataVar)
latVar = netcdfUtils.findLatitudeVar(nc, dataVar)
timeVar=netcdfUtils.findTimeVar(nc,dataVar)
zVar=netcdfUtils.findVerticalVar(nc,dataVar)
timeVal=timeVar[:]
# check if the longitude, latitude or the time dimension is abscent and raise error
if lonVar is None or latVar is None or timeVar is None:
raise ValueError("Cannot extract map data if longitude, latitude and time dimensios are abscent")
# map the longitutude value from range (-180 to 180) onto (0 to 360) in the data file
#lonVal=lonVal+180
if min(lonVar[:])>=0:
if lonVal<0:
lonVal=lonVal+180
# if the dimensions are 4 i.e. time,vertical,latitude and longitude
if numDims == 4:
#get the vertical,longitude and latitude indices
lonIndex=utils.findNearestIndex(lonVar,lonVal)
latIndex=utils.findNearestIndex(latVar,latVal)
zIndex=utils.findNearestIndex(zVar,zVal)
return dataVar[:,zIndex,latIndex,lonIndex],timeVal
# if the dimensions are 3 ie time, latitude and longitude
elif numDims == 3:
#get the longitude and latitude indices
lonIndex=utils.findNearestIndex(lonVar,lonVal)
latIndex=utils.findNearestIndex(latVar,latVal)
return dataVar[:,latIndex,lonIndex],timeVal
def findNearestLatIndex(nc,dataVar,latVal):
""" Searches through latitude values for the target value,using the findLatitudeVar() in
netcdfUtils module and the findNearestIndex() function from the utils module, returning
the index of the latitude value that is closest numerically to the target value. If more
than one latitude value is equally close to the target, the index of the first value will
be returned. If the Latitude dimension does not exit a error is raised """
import utils
#check if the latitude value is within the latitude range
if latVal>90 or latVal<-90:
raise ValueError("The value entered is ouside latitude range of values +90 to -90")
# check if the Variable object representing the latitude axis exists in the netcdf file
coordVar=findLatitudeVar(nc,dataVar)#returns Variable object representing latitude axis for the data variable
if coordVar is None:
raise ValueError("No Variable object for the latitude axis exists in the netcdf file")
else:
#get an array of latitude values from where to search for the given latitude value
latVals=coordVar[:]
#find the index of the given latitude value
latIndex=utils.findNearestIndex(latVals,latVal)
return latIndex #latitude index value
def findNearestZIndex(nc,dataVar,zVal):
""" Searches through vertical axis values for the target value,using the findVerticalVar()
in netcdfUtils module and the findNearestIndex() function from the utils module, returning
the index of the vertical axis value that is closest numerically to the target value. If
more than one latitude value is equally close to the target, the index of the first value
will be returned.If the vertical dimension does not exit an error is raised """
import utils
# check if the Variable object representing the vertical axis exists in the netcdf file
coordVal=findVerticalVar(nc,dataVar)#returns Variable object representing vertical axis for the data variable
if coordVal is None:
raise ValueError("No Variable object for the vertical axis exists in the netcdf file")
else:
#get an array of vertical values from where to search for the given vertical value
zVals=coordVal[:]
#check if the vertical value given is within the vertical axis range of values
if zVal<zVals[0] or zVal>max(zVals):
raise ValueError("The value entered is ouside vertical coordinate range of values")
#find the index of the given vertical axis value
zIndex=utils.findNearestIndex(zVals,zVal)
#return the index of the vertical value
return zIndex
