[Numpy-discussion] netcdf lat lon to coord - ValueError: need more than 1 value to unpack

questions anon questions.anon at gmail.com
Tue Mar 24 16:10:00 EDT 2015


perfect, thank you!

On Tue, Mar 24, 2015 at 9:14 PM, Kiko <kikocorreoso at gmail.com> wrote:

>
>
> 2015-03-24 11:02 GMT+01:00 questions anon <questions.anon at gmail.com>:
>
>> I would like to find the nearest coord in a netcdf from a given latitude
>> and longitude.
>> I found some fantastic code that does this -
>> http://nbviewer.ipython.org/github/Unidata/unidata-python-workshop/blob/master/netcdf-by-coordinates.ipynb
>> but I keep receiving this error - I am receiving a ValueError: need more
>> than 1 value to unpack
>>
>> I have pasted the code and full error below. Any help will be greatly
>> appreciated.
>>
>>
>>
>>
>> import numpy as np
>>
>> import netCDF4
>>
>>
>> def naive_fast(latvar,lonvar,lat0,lon0):
>>
>>    # Read latitude and longitude from file into numpy arrays
>>
>>    latvals = latvar[:]
>>
>>    lonvals = lonvar[:]
>>
>>    ny,nx = latvals.shape
>>
>>    dist_sq = (latvals-lat0)**2 + (lonvals-lon0)**2
>>
>>    minindex_flattened = dist_sq.argmin() # 1D index of min element
>>
>>    iy_min,ix_min = np.unravel_index(minindex_flattened, latvals.shape)
>>
>>    return iy_min,ix_min
>>
>> filename = "/Users/T_SFC.nc"
>>
>> ncfile = netCDF4.Dataset(filename, 'r')
>>
>> latvar = ncfile.variables['latitude']
>>
>> lonvar = ncfile.variables['longitude']
>>
>>
>> iy,ix = naive_fast(latvar, lonvar, -38.009, 146.438)
>>
>> print 'Closest lat lon:', latvar[iy,ix], lonvar[iy,ix]
>>
>> ncfile.close()
>>
>>
>>
>>
>>
>>
>> ---------------------------------------------------------------------------
>> ValueError                                Traceback (most recent call
>> last)
>> /Applications/Canopy.app/appdata/canopy-1.3.0.1715.macosx-x86_64/Canopy.app/Contents/lib/python2.7/site-packages/IPython/utils/py3compat.pyc
>> in execfile(fname, *where)
>>     202             else:
>>     203                 filename = fname
>> --> 204             __builtin__.execfile(filename, *where)
>>
>> /Users/latlon_to_closestgrid.py in <module>()
>>      22 lonvar = ncfile.variables['longitude']
>>      23
>> ---> 24 iy,ix = naive_fast(latvar, lonvar, -38.009, 146.438)
>>      25 print 'Closest lat lon:', latvar[iy,ix], lonvar[iy,ix]
>>      26 ncfile.close()
>>
>> /Users/latlon_to_closestgrid.py in naive_fast(latvar, lonvar, lat0, lon0)
>>      12     latvals = latvar[:]
>>      13     lonvals = lonvar[:]
>> ---> 14     ny,nx = latvals.shape
>>      15     dist_sq = (latvals-lat0)**2 + (lonvals-lon0)**2
>>      16     minindex_flattened = dist_sq.argmin()  # 1D index of min
>> element
>>
>> ValueError: need more than 1 value to unpack
>>
>>
>>
> It seems that latvals and lonvals should be a 2D array and you are
> providing just a 1D array.
> Maybe you could use numpy.meshgrid [1] to get 2D inputs from 1D arrays.
>
> [1]
> http://docs.scipy.org/doc/numpy/reference/generated/numpy.meshgrid.html
>
>
>>
>>
>>
>>
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>>
>
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