[AstroPy] Ellipse2D fit

[Andrzej Szary]

Dear Fabricio,

Note that the DATA and MODEL parameters are different. For a good fit they
should be similar. You can get better results using different fitter (*fi =
fitting.SimplexLSQFitter()*), but it is still not good enough for my
purpose (I need to find theta parameter).

Best wishes
Andrzej Szary


>> On 15 February 2017 at 13:14, Fabricio Ferrari <
fabricio.ferrari at gmail.com> wrote:
>>
>> Dear Andrzej
>>
>> here it seemed to work. Maybe the version you are using.
>>
>> Here I have:
>>
>>In [2]: np.__version__
>>Out[2]: '1.11.1'
>>
>>In [4]: astropy.__version__
>>Out[4]: u'1.2.1'
>>
>>My output:
>>
>>DATA:
>>Model: Ellipse2D
>>Inputs: (u'x', u'y')
>>Outputs: (u'z',)
>>Model set size: 1
>>Parameters:
>>    amplitude x_0 y_0  a   b  theta
>>    --------- --- --- --- --- -----
>>          1.0 0.0 0.0 2.0 1.0   0.0
>>
>>
>>MODEL:
>>Model: Ellipse2D
>>Inputs: (u'x', u'y')
>>Outputs: (u'z',)
>>Model set size: 1
>>Parameters:
>>      amplitude    x_0 y_0  a   b  theta
>>    -------------- --- --- --- --- -----
>>    0.338211382114 0.1 0.1 3.0 2.0   0.2
>>
>>p.s. thank you for letting me know about the Ellipse2D fit, that I indeed
need and did not >>know about.
>>
>>Regards
>>Fabricio


On 8 February 2017 at 16:40, Andrzej Szary <aszary at gmail.com> wrote:

> Hello,
>
> I am struggling with  fitting an ellipse using Ellipse2D model. The
> fitting procedure does not seem to have any effect on ellipse parameters
> (maybe except amplitude).
>
> Please find a test code at the end of this email.
>
> Best wishes,
> Andrzej Szary
>
>
> import numpy as np
> from astropy.modeling import models, fitting
> import matplotlib.pyplot as pl
>
> # data
> num = 100
> x, y = np.meshgrid(np.linspace(-5., 5., num), np.linspace(-5, 5, num))
> e0 = models.Ellipse2D(amplitude=1., x_0=0., y_0=0., a=2, b=1, theta=0.)
> z0 = e0(x, y)
> print 'DATA:\n', e0, '\n\n'
>
> # initial model
> ei = models.Ellipse2D(amplitude=1., x_0=0.1, y_0=0.1, a=3, b=2, theta=0.2)
> fi = fitting.LevMarLSQFitter()
>
> # fitted model?
> e1 = fi(ei, x, y, z0)
> z1 = e1(x, y)
> print 'MODEL:\n', e1, '\n\n'
>
> pl.imshow(z0, extent=[-5, 5, -5, 5], alpha=0.5)
> pl.imshow(z1, extent=[-5, 5, -5, 5], alpha=0.2)
> pl.show()
>
>
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