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Geo divide zero #505

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Oct 4, 2011
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Geo divide zero #505

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1391ad0
geo.py: prevent division by zero in Mollweide transform
efiring Oct 2, 2011
533e5fb
geo.py: fix divide-by-zero warning in Aitoff transform
efiring Oct 2, 2011
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geo.py: fix divide-by-zero warning in Aitoff transform 
An attempt to do this had been make by masking zero values
in the denominator; but at least with current numpy, this is
not enough, because the __div__ method of the first argument
is used.  The solution is to ensure that the first argument
is also a masked array.
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@efiring
efiring committed Oct 2, 2011
commit 533e5fba0bee341bec31bb2987c19e86b05cb631
12 changes: 6 additions & 6 deletions lib/matplotlib/projections/geo.py
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Expand Up @@ -271,16 +271,16 @@ def transform(self, ll):
cos_latitude = np.cos(latitude)

alpha = np.arccos(cos_latitude * np.cos(half_long))
# Mask this array, or we'll get divide-by-zero errors
# Mask this array or we'll get divide-by-zero errors
alpha = ma.masked_where(alpha == 0.0, alpha)
# The numerators also need to be masked so that masked
# division will be invoked.
# We want unnormalized sinc. numpy.sinc gives us normalized
sinc_alpha = ma.sin(alpha) / alpha

x = (cos_latitude * np.sin(half_long)) / sinc_alpha
y = (np.sin(latitude) / sinc_alpha)
x.set_fill_value(0.0)
y.set_fill_value(0.0)
return np.concatenate((x.filled(), y.filled()), 1)
x = (cos_latitude * ma.sin(half_long)) / sinc_alpha
y = (ma.sin(latitude) / sinc_alpha)
return np.concatenate((x.filled(0), y.filled(0)), 1)
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Is it right that we have np.cos(latitude) in the numerator on 282 but ma.sin(latitude) in the numerator on 283?

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Yes.
http://en.wikipedia.org/wiki/Aitoff_projection
The one difference is the factor of 2 in x; but it is handed via set_aspect in the init() method.

transform.__doc__ = Transform.transform.__doc__

transform_non_affine = transform
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