Percentile function sometimes returns 'nan'

[rickemery]

The Percentile function of GeoRaster will sometimes, but not always, return 'nan'.

Setup:

p = ProjectInventory('/scratch/bziniti/percentile_test/')
date = datetime.date(2010, 7, 15)
band = p[date].open('ref-masked-tsi-mod2-cla4')[0]

Example of issue:

In [36]: band.Percentile(95.0)
Out[36]: 3.0

In [37]: band.Percentile(95.0)
Out[37]: 3.0

In [38]: band.Percentile(95.0)
Out[38]: nan

In [39]: band.Percentile(95.0)
Out[39]: 3.0

In [40]: band.Percentile(95.0)
Out[40]: 3.0