netcdf lat lon to coord - ValueError: need more than 1 value to unpack
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/mast... 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
2015-03-24 11:02 GMT+01:00 questions anon <questions.anon@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/mast... 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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perfect, thank you! On Tue, Mar 24, 2015 at 9:14 PM, Kiko <kikocorreoso@gmail.com> wrote:
2015-03-24 11:02 GMT+01:00 questions anon <questions.anon@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/mast... 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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