"Not JSON compliant number" building a geojson file

Question

I'm trying to build a GeoJSON file with Python geojson module consisting on a regular 2-d grid of points whose 'properties' are associated to geophysical variables (velocity,temperature, etc). The information comes from a netcdf file.

So the code is something like that:

from netCDF4 import Dataset
import numpy as np
import geojson

ncfile = Dataset('20140925-0332-n19.nc', 'r')
u = ncfile.variables['Ug'][:,:] # [T,Z,Y,X]
v = ncfile.variables['Vg'][:,:]
lat = ncfile.variables['lat'][:]
lon = ncfile.variables['lon'][:]

features=[]
for i in range(0,len(lat)):
     for j in range(0,len(lon)):
         coords = (lon[j],lat[i])
         features.append(geojson.Feature(geometry = geojson.Point(coords),properties={"u":u[i,j],"v":v[i,j]}))

In this case the point has velocity components in the 'properties' object. The error I receive is on the features.append() line with the following message:

*ValueError: -5.4989638 is not JSON compliant number*

which corresponds to a longitude value. Can someone explains me whatcan be wrong ?

The only code in the geojson module which corresponds to your error is found here: https://github.com/frewsxcv/python-geojson/blob/bfea4a814632806761093eafcd50de27ec013de7/geojson/geometry.py#L35-L40 Can you try a `class(velocity).__name__` to see what the class of your velocity number is? — bretmattingly, Jun 13 '16 at 18:57

score 2 · Answer 1 · answered Dec 31 '17 at 00:18

2

I have used simply conversion to float and it eliminated that error without need of numpy.

coords = (float(lon[j]),float(lat[i]))

answered Dec 31 '17 at 00:18

vhaska

66
7

score 1 · Answer 2 · edited May 23 '17 at 12:08

I found the solution. The geojson module only supports standard Python data classes, while numpy extends up to 24 types. Unfortunately netCDF4 module needs numpy to load arrays from netCDF files. I solved using numpy.asscalar() method as explained here. So in the code above for example:

  coords = (lon[j],lat[i])

is replaced by

  coords = (np.asscalar(lon[j]),np.asscalar(lat[i]))

and works also for the rest of variables coming from the netCDF file. Anyway, thanks Bret for your comment that provide me the clue to solve it.

"Not JSON compliant number" building a geojson file

2 Answers2