[Branch]: differential_rotation

This is the feature branch that contains some diff rot code, I think it needs some love so I am opening this so people don't forget about it!!
Informative errors are good, but as I said, this will add a lot more if
blocks in the code:

if _is_quantity(input_parameters):
   ....code that I don't think should be in an if block
else:
  ValueError('shoulda used quantities')

I am not sure that the added complexity in every piece of code is worth it.




On Tue, Nov 4, 2014 at 5:10 PM, Stuart Mumford <notifications@github.com>
wrote:

> In sunpy/image/coalignment.py:
>
> > @@ -44,6 +46,18 @@ def _default_fmap_function(data):
> >      return np.float64(data)
> >
> >
> > +def _is_pixel_unit(a):
> > +    """Tests the input to see if it is an astropy Quantity with units in
> > +    pixels."""
> > +    return (isinstance(a, u.Quantity) and a.unit == 'pix')
> > +
> > +
> > +def _is_arcsec_unit(a):
> > +    """Tests the input to see if it is an astropy Quantity with units in
> > +    arcseconds."""
> > +    return (isinstance(a, u.Quantity) and a.unit == 'arcsec')
>
> I think we probably need a utility function for it so that it is easier to
> do everywhere, the thing with Quantities is because they are so similar to
> floats, also very specific, and new I think it is very important to give
> the user informative errors.
>
> --
> Reply to this email directly or view it on GitHub
> <https://github.com/sunpy/sunpy/pull/902/files#r19840204>.
>