medians for degree measurements

Robert Kern robert.kern at gmail.com
Mon Jan 25 18:39:04 CET 2010


On 2010-01-25 11:06 AM, Bas wrote:
>> On 2010-01-25 10:16 AM, Bas wrote:
>>
>>> P.S.
>>> Slightly off-topic rant against both numpy and matlab implementation
>>> of unwrap: They always assume data is in radians. There is some option
>>> to specify the maximum jump size in radians, but to me it would be
>>> more useful to specify the interval of a complete cycle, so that you
>>> can do
>>
>>> unwrapped_radians = unwrap(radians)
>>> unwrapped_degrees = unwrap(degrees, 360)
>>> unwrapped_32bit_counter = unwrap(overflowing_counter, 2**32)
>
> On Jan 25, 5:34 pm, Robert Kern<robert.k... at gmail.com>  wrote:>
>> Rants accompanied with patches are more effective. :-)
>
> As you wish (untested):
>
> def unwrap(p, cycle=2*pi, axis=-1):
>      """docstring to be updated"""
>      p = asarray(p)
>      half_cycle = cycle / 2
>      nd = len(p.shape)
>      dd = diff(p, axis=axis)
>      slice1 = [slice(None, None)]*nd     # full slices
>      slice1[axis] = slice(1, None)
>      ddmod = mod(dd+half_cycle, cycle)-half_cycle
>      _nx.putmask(ddmod, (ddmod==-half_cycle)&  (dd>  0), half_cycle)
>      ph_correct = ddmod - dd;
>      _nx.putmask(ph_correct, abs(dd)<half_cycle, 0)
>      up = array(p, copy=True, dtype='d')
>      up[slice1] = p[slice1] + ph_correct.cumsum(axis)
>      return up
>
> I never saw a use case for the discontinuity argument, so in my
> preferred version it would be removed. Of course this breaks old code
> (by who uses this option anyhow??) and breaks compatibility between
> matlab and numpy.

Sometimes legitimate features have phase discontinuities greater than pi. If you 
want your feature to be accepted, please submit a patch that does not break 
backwards compatibility and which updates the docstring and tests appropriately. 
I look forward to seeing the complete patch! Thank you.

   http://projects.scipy.org/numpy

-- 
Robert Kern

"I have come to believe that the whole world is an enigma, a harmless enigma
  that is made terrible by our own mad attempt to interpret it as though it had
  an underlying truth."
   -- Umberto Eco




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