Hi All,
The problem is not with fetching the data slice itself, but finding the
correct indices to specify, particularly with the time dimension. The
below examples refer to a remote dataset that I can open and slice using
indices, as in
slice = remoteobj.variables['tas'][:120,20:40,30:50].
However, I have problems when trying to use the syntax in plotsst.py or
pnganim.py (from the examples) to find time indices:
In [107]: from datetime import datetime as dt
In [108]: date0 = dt(1951,1,1,0)
In [110]: print date0
1951-01-01 00:00:00
In [125]: timedata = remoteobj.variables['time']
In [126]: nt0 = date2index(date0,timedata)
---------------------------------------------------------------------------
AssertionError Traceback (most recent call last)
/home/amg/work/nhmm/<ipython console> in <module>()
/usr/local/cdat/trunk/lib/python2.5/site-packages/mpl_toolkits/basemap/__init__.pyc
in date2index(dates, nctime, calendar)
3924 Returns an index or a sequence of indices.
3925 """
-> 3926 return netcdftime.date2index(dates, nctime, calendar=None)
3927
3928 def maskoceans(lonsin,latsin,datain,inlands=False):
/usr/local/cdat/trunk/lib/python2.5/site-packages/mpl_toolkits/basemap/netcdftime.pyc
in date2index(dates, nctime, calendar)
986
987 # Perform check again.
--> 988 _check_index(index, dates, nctime, calendar)
989
990 # convert numpy scalars or single element arrays to python
ints.
/usr/local/cdat/trunk/lib/python2.5/site-packages/mpl_toolkits/basemap/netcdftime.pyc
in _check_index(indices, dates, nctime, calendar)
941 for n,i in enumerate(indices):
942 t[n] = nctime[i]
--> 943 assert numpy.all( num2date(t, nctime.units, calendar) == dates)
944
945
AssertionError:
---------------------------------------------------------
It turns out that date0 corresponds best to index 1080:
In [139]: remoteobj.variables['time'][1080]
Out[139]: 32865.5
In [141]: num2date(32865.5,timedata.units,timedata.calendar)
Out[141]: 1951-01-16 12:00:00
This isn't the _exact_ date and time I had specified, but
In [142]: date0 = dt(1951,01,16,12,00,00)
In [143]: print date0
1951-01-16 12:00:00
In [144]: date2index(date0,timedata,timedata.calendar)
produces the same AssertionError. Where is the problem?
What I would _like_ to do is to issue a simple call using coordinates
rather than the indices, of the form:
slice = variable[date0:date1,[plev],lat0:lat1,lon0:lon1],
or similar, preferably without writing a whole module just to find the
correct indices. I need to fetch similar slices from a group of models,
having time axes that may each be defined slightly differently --
different calendars, time point set at a different day of the month,
etc. (It's monthly data and I'm specifying only monthly bounds, even
though the calendar may be defined as "days since 1860...") I need to
automate the process so I get back the correct slab regardless.
Suggestions appreciated!
Thx,
Arthur
*^*~*^*~*^*~*^*~*^*~*^*~*^*~*^*~*^*~*^*~*^*~*^*~*^*~*^*~*^*~*
Arthur M. Greene, Ph.D.
The International Research Institute for Climate and Society (IRI)
The Earth Institute, Columbia University, Lamont Campus
amg at iri dot columbia dot edu | http://iri.columbia.edu
*^*~*^*~*^*~*^*~*^*~*^*~*^*~*^*~*^*~*^*~*^*~*^*~*^*~*^*~*^*~*
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