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romh

29 Apr 2023 05:41



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Colectia asta de librarii nu e chiar asa de inutila. O sa incerc sa pun niste exemple cu tot felul de experimente pe care le fac si care sper ca pot fi utile pentru alti amatori. Iar notebookurile sunt simple tutoriale gasite online si adaptate un pic la nevoile unui amator.

Fotometrie

Este procesul de masurare a intensitatii si luminozitatii printre altele si pentru calculul magnitudinii aparente
Vom folosi libraria Photutils din colectia Astropy pentru a identifica stelele dintr-o poza jpeg si apoi vom plota si coordonatele acestei stele.

Utilitate:

- Extragerea de informatii din pozele astronomilor amatori
- Detectarea de duble
- Calculul magnitudinii aparente

Principala provocare o reprezinta faptul ca nu lucrez .. inca cu poze fips. E un format pe care trebuie sa il inteleg mai bine. Dar am vrut sa iau o poza jpeg facuta cu telefonul acum ceva timp si sa vad daca reusesc sa extrag stelele. As putea sa fac ceva simplu dar libraria de mai sus deja foloseste niste modele citate de tipi de la nasa... imi imaginez ca e mai buna decat orice pot sa inventez eu.

Notebookul Jupyter se gaseste aici, puteti sa rulati toate celulele si sa le analizati dupa
https://colab.research.google.com/drive/1ahaoy01WA64aKty7_u0xYOnCSzp7Bokc?usp=sharing

Modelul de detectie se numeste daostarfinder. pare sa fie cel putin 3 alte modele. 


    

    Detect stars in an image using the DAOFIND (`Stetson 1987
    <https>`_)
    algorithm.

    DAOFIND (`Stetson 1987; PASP 99, 191
    <https>`_)
    searches images for local density maxima that have a peak amplitude
    greater than ``threshold`` (approximately; ``threshold`` is applied
    to a convolved image) and have a size and shape similar to the
    defined 2D Gaussian kernel.  The Gaussian kernel is defined by the
    ``fwhm``, ``ratio``, ``theta``, and ``sigma_radius`` input
    parameters.

    ``DAOStarFinder`` finds the object centroid by fitting the marginal x
    and y 1D distributions of the Gaussian kernel to the marginal x and
    y distributions of the input (unconvolved) ``data`` image.

    ``DAOStarFinder`` calculates the object roundness using two methods. The
    ``roundlo`` and ``roundhi`` bounds are applied to both measures of
    roundness.  The first method (``roundness1``; called ``SROUND`` in
    `DAOFIND`_) is based on the source symmetry and is the ratio of a
    measure of the object's bilateral (2-fold) to four-fold symmetry.
    The second roundness statistic (``roundness2``; called ``GROUND`` in
    `DAOFIND`_) measures the ratio of the difference in the height of
    the best fitting Gaussian function in x minus the best fitting
    Gaussian function in y, divided by the average of the best fitting
    Gaussian functions in x and y.  A circular source will have a zero
    roundness.  A source extended in x or y will have a negative or
    positive roundness, respectively.

    The sharpness statistic measures the ratio of the difference between
    the height of the central pixel and the mean of the surrounding
    non-bad pixels in the convolved image, to the height of the best
    fitting Gaussian function at that point.

    Parameters
    ----------
    threshold : float
        The absolute image value above which to select sources.

    fwhm : float
        The full-width half-maximum (FWHM) of the major axis of the
        Gaussian kernel in units of pixels.


.... blablabla



Atasez si rezultatul final mai jos, dar mai importante sunt tabelele cu magnitudini... Nu pare sa reflecteze realitatea din cauza limitarilor cmos dar inca nu am verificat bine lucrul asta. Poate cand imi vine housingul la camera usb.

As vrea sa gasesc si o modalitate de a adauga legenda cu coordonate, dar inca nu am gasit o cale.


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https://photutils.readthedocs.io/en/stable/