python将OpenDap加载到NetcdfFile

Question

我使用URL从opendap服务器(数据的子集)打开netcdf数据。当我打开它时，数据(据我所见)直到变量被请求时才被实际加载。我想要将数据保存到磁盘上的文件中，我该如何操作？

我目前有：

import numpy as np
import netCDF4 as NC

url = u'http://etc/etc/hourly?varname[0:1:10][0:1:30]'
set = NC.Dataset(url) # I think data is not yet loaded here, only the "layout"
varData = set.variables['varname'][:,:] # I think data is loaded here

# now i want to save this data to a file (for example test.nc), set.close() obviously wont work

希望有人能帮上忙，谢谢！

Answer 1

它非常简单；创建一个新的NetCDF文件，然后复制您想要的任何东西:)幸运的是，在复制正确的尺寸、NetCDF属性时，这可以在很大程度上自动完成。从输入文件中。我快速地编写了这个示例，输入文件也是一个本地文件，但是如果使用OPenDAP的读取已经正常工作，它应该会以类似的方式工作。

import netCDF4 as nc4

# Open input file in read (r), and output file in write (w) mode:
nc_in = nc4.Dataset('drycblles.default.0000000.nc', 'r')
nc_out = nc4.Dataset('local_copy.nc', 'w')

# For simplicity; copy all dimensions (with correct size) to output file
for dim in nc_in.dimensions:
    nc_out.createDimension(dim, nc_in.dimensions[dim].size)

# List of variables to copy (they have to be in nc_in...):
# If you want all vaiables, this could be replaced with nc_in.variables
vars_out = ['z', 'zh', 't', 'th', 'thgrad']

for var in vars_out:
    # Create variable in new file:
    var_in  = nc_in.variables[var]
    var_out = nc_out.createVariable(var, datatype=var_in.dtype, dimensions=var_in.dimensions)

    # Copy NetCDF attributes:
    for attr in var_in.ncattrs():
        var_out.setncattr(attr, var_in.getncattr(attr))

    # Copy data:
    var_out[:] = var_in[:]

nc_out.close()

希望它能帮上忙，如果不能，请告诉我。

Answer 2

如果你可以使用xarray，它应该是这样工作的：

import xarray as xr

url = u'http://etc/etc/hourly?varname[0:1:10][0:1:30]'
ds = xr.open_dataset(url, engine='netcdf4')  # or engine='pydap'
ds.to_netcdf('test.nc')

xarray documentation提供了另一个示例来说明如何做到这一点。