[AstroPy] Gaussian models fitter non-functional?

[José Vinícius]

Hi all,

On 10/16/15 9:47 AM, Giuliano Iorio wrote:

> It can be also that the image is too noisy around the target to fit. I
> usually use only a little subarray around the target, then I search the
> position of the maximum and I set the initial guess of xo and yo to its
> position. After I normalize all the subarray to the value of the maximum
> and cut all the signal below a certain threshold (usually 0.1).
> In this way I am able to obtain a robust fit also in very noisy map.


​That's an interesting approach, I'm going to give it a try.​

​

Another clever approach too, which I have used to calculate initial guesses
for maximum likelihood estimators (which usually needs a rather closer
initial guess than least squares), is simply to take the centroid of the
amplitudes in the region of interest. It's fairly robust even in very noisy
(poisson + gaussian) scenarios.

Cheers,
-Jose.

CVLattes: http://lattes.cnpq.br/3267230342393209

On Sat, Oct 17, 2015 at 12:15 AM, banyal <banyal at iiap.res.in> wrote:

> Hi Jeff,
>
> The  fits data  is located in  hdulist[1].data and not in hdulist[0].data
>
> g = fit_g(g_init, xx, yy, hdulist[1].data)     instead of
>
> g = fit_g(g_init, xx, yy, hdulist[0].data)
>
>
> -Ravi
>
> On 2015-10-16 19:06, Jeff Mangum wrote:
>
> Thank you Steve.  I mis-typed.  Yes, "g" is where the fit should be.
> Unfortunately, it is equal to g_init:
>
> In [304]: g
> Out[304]: <Gaussian2D(amplitude=1.0, x_mean=55.873445625871355,
> y_mean=55.410802834496835, x_stddev=1.0, y_stddev=1.0, theta=0.0)>
>
> Still looks to me like the fitter is not fitting...
>
> -- Jeff
>
>
> On 10/16/15 9:28 AM, Steve Crawford wrote:
>
> Hi Jeff-- The fitted model will not be in g_init (this remains unchanged),
> but in g. If you take a look in g, you should be able to see the fitted
> results. Cheers Steve ----- Original Message ----- From: "Jeff Mangum" <
> jmangum at nrao.edu> To: astropy at scipy.org Sent: Friday, October 16, 2015
> 3:11:56 PM Subject: [AstroPy] Gaussian models fitter non-functional? Hello,
> Long-time listener but first-time caller. Have been trying to use the 2D
> Gaussian fitting capabilities within astropy.models to fit a 2D Gaussian to
> an image (in FITS format). Here is my script: import numpy as np import
> radio_beam from astropy.modeling import models, fitting from astropy import
> units as u from astropy.io import fits import astropy.coordinates as
> coord import astropy.wcs as wcs import matplotlib import pylab as pl # The
> following is the position of the peak in both J1 and J2, so use # it as the
> starting guess ra0 = '13h15m03.50s' dec0 = '24d37m08.2s' radeg =
> coord.Angle(ra0, unit=u.hour).degree decdeg = coord.Angle(dec0,
> unit=u.degree) # Now open the image hdulist =
> fits.open('IC860CbandCarrayH2COJ1_moment0.fits') #hdulist =
> fits.open('IC860KubandDarrayH2COJ2_moment0.fits') w =
> wcs.WCS(hdulist[0].header, hdulist) yy,xx =
> np.indices(hdulist[0].data.shape) x0,y0 = w.wcs_world2pix(radeg, decdeg, 1)
> # Now fit 2D gaussian g_init = models.Gaussian2D(amplitude=1., x_mean=x0,
> y_mean=y0, x_stddev=1, y_stddev=1) fit_g = fitting.LevMarLSQFitter() g =
> fit_g(g_init, xx, yy, hdulist[0].data) When I look at g_init (which is
> where I believe the fit results should be), I see that the fit has not
> moved from its initial settings. It appears that the fitter just did not
> run. With Adam Ginsburg's help I have a workaround using gaussfitter, but
> would certainly like to make this work with astropy.models. Thanks! -- Jeff
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