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Doc: Added :param: role for SExtractor measurements parameters and modified... 

Doc: Added :param: role for SExtractor measurements parameters and modified custom CSS to manage the :param: role.
Doc: Added targetparam class and setup targets in preliminary measurement parameter list.
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doc/src/Param.rst
View file @ e8f9a2ae
.. File Param.rst
.. include:: global.rst
The measurement (or catalog) parameter file
===========================================
In addition to the configuration file detailed above, |SExtractor| requires a file containing the list of measurements ("catalog parameters") that will be listed in the output catalog for every detection. This allows the software to compute only the measurements that are needed. The name of this catalog parameter file is traditionally suffixed with ``.param``, and must
be specified using the ``PARAMETERS_NAME`` config parameter. The full set
of parameters can be queried with the command
In addition to the configuration file detailed above, |SExtractor| requires a file containing the list of measurements ("catalog parameters") that will be listed in the output catalog for every detection. This allows the software to compute only the measurements that are needed. The name of this catalog parameter file is traditionally suffixed with ``.param``, and must be specified using the :param:`PARAMETERS_NAME` config parameter. The full set of parameters can be queried with the command
.. code-block:: console
......@@ -16,11 +16,11 @@ Format
The format of the catalog parameter list is ASCII, and there must be
*a single keyword per line*. Presently two kinds of keywords are
recognized by |SExtractor|: scalars and vectors. Scalars, like ``X_IMAGE``,
produce single numbers in the output catalog. Vectors, like ``MAG_APER(4)``
or ``VIGNET(15,15)``, produce arrays of numbers. The ordering of measurements
recognized by |SExtractor|: scalars and vectors. Scalars, like :param:`X_IMAGE`,
produce single numbers in the output catalog. Vectors, like :param:`MAG_APER(4)`
or :param:`VIGNET(15,15)`, produce arrays of numbers. The ordering of measurements
in the output catalog is identical to that of the keywords in the parameter
list. Comments are allowed, they must begin with a ``#``.
list. Comments are allowed, they must begin with a :param:`#`.
Variants
--------
......@@ -32,10 +32,7 @@ available:
Fluxes
~~~~~~
Fluxes may be expressed in linear (ADU) units or as Pogson
:cite:`1856MNRAS_17_12P` magnitudes. Flux measurements in ADUs
are prefixed with ``FLUX_``, for example: ``FLUX_AUTO``, ``FLUX_ISO``, etc.
Magnitudes are prefixed with ``MAG_`` e.g., ``MAG_AUTO``, ``MAG_ISO``, ... In
Fluxes may be expressed in linear (ADU) units or as Pogson :cite:`1856MNRAS_17_12P` magnitudes. Flux measurements in ADUs are prefixed with :param:`FLUX_`, for example: :param:`FLUX_AUTO`, :param:`FLUX_ISO`, etc. Magnitudes are prefixed with :param:`MAG_` e.g., :param:`MAG_AUTO`, :param:`MAG_ISO`, ... In
|SExtractor| the magnitude :math:`m` of a source is derived from the flux
:math:`f`:
......@@ -52,11 +49,7 @@ where :math:`m_{ZP}` is the magnitude zero-point set with the
Flux uncertainties
~~~~~~~~~~~~~~~~~~
Flux uncertainties follow a scheme similar to that of fluxes. Flux uncertainties are
prefixed with ``FLUXERR_``, as in ``FLUXERR_AUTO`` or ``FLUXERR_ISO``. Magnitude
uncertainties start with ``MAGERR_``, for instance: ``MAGERR_AUTO``,
``MAGERR_ISO``,... Magnitude uncertainties :math:`\sigma_m` are derived
from the estimated 1-\ :math:`\sigma` flux error :math:`\sigma_f`:
Flux uncertainties follow a scheme similar to that of fluxes. Flux uncertainties are prefixed with :param:`FLUXERR_`, as in :param:`FLUXERR_AUTO` or :param:`FLUXERR_ISO`. Magnitude uncertainties start with :param:`MAGERR_`, for instance: :param:`MAGERR_AUTO`, :param:`MAGERR_ISO`,... Magnitude uncertainties :math:`\sigma_m` are derived from the estimated 1-\ :math:`\sigma` flux error :math:`\sigma_f`:
.. math::
......@@ -72,14 +65,14 @@ Positions and shapes
Positions, distances and position angles are computed in pixel coordinates. They may be expressed in image pixels, world coordinates, or in celestial coordinates, depending on the suffix:
_IMAGE
Measurements are given in pixel coordinates, in units of pixels. For example: ``Y_IMAGE``, ``ERRAWIN_IMAGE``, ``THETA_IMAGE`` etc. Following the FITS convention, in |SExtractor| the center of the first image pixel has coordinates (1.0,1.0). Position angles are counted from the *x* axis (axis 1), positive towards the *y* axis (axis 2)
:param:`_IMAGE`
Measurements are given in pixel coordinates, in units of pixels. For example: :param:`Y_IMAGE`, :param:`ERRAWIN_IMAGE`, :param:`THETA_IMAGE` etc. Following the FITS convention, in |SExtractor| the center of the first image pixel has coordinates (1.0,1.0). Position angles are counted from the *x* axis (axis 1), positive towards the *y* axis (axis 2)
_WORLD
:param:`_WORLD`
Measurements are given in so-called “world coordinates”, converted from pixel coordinates using the local Jacobian of the transformation between both systems. This requires World Coordinate System (|WCS|_) metadata :cite:`2002AA_395_1061G` to be present in the FITS image header(s). Position angles are counted from the first world axis, positive towards the second world axis.
_SKY, _J2000, _B1950
Measurements are given in celestial (equatorial) coordinates, converted from pixel coordinates using the local Jacobian of the transformation between both systems. Positions and distances are in units of degrees. This requires celestial |WCS| metadata :cite:`2002AA_395_1077C` to be present in the FITS image header(s). _SKY measurements are given in the native world coordinate system. _J2000 and _B1950 measurements are automatically converted from the native |WCS|, taking into account the change of reference frame. In all cases, positions angles are counted East-of-North.
:param:`_SKY`, :param:`_J2000`, :param:`_B1950`
Measurements are given in celestial (equatorial) coordinates, converted from pixel coordinates using the local Jacobian of the transformation between both systems. Positions and distances are in units of degrees. This requires celestial |WCS| metadata :cite:`2002AA_395_1077C` to be present in the FITS image header(s). :param:`_SKY` measurements are given in the native world coordinate system. :param:`_J2000` and :param:`_B1950` measurements are automatically converted from the native |WCS|, taking into account the change of reference frame. In all cases, positions angles are counted East-of-North.
Measurement parameter list
--------------------------
......@@ -89,14 +82,19 @@ Below is an exhaustive list of all the measurement parameters known to
of their meaning.
.. csv-table:: |SExtractor| measurement parameters
:class: targetparam
:header: "Name", "Unit", "Description"
:widths: 15 10 30
NUMBER,, Running object number
ID_PARENT,..., Parent ID (before deblending)
EXT_NUMBER,..., FITS extension number
:ref:`FLUX_ISO<flux_iso>`, count, Isophotal flux
:ref:`FLUXERR_ISO<flux_iso>`, count, RMS error estimate for isophotal flux
.. include:: keys.rst
_`FLUX_ISO`, count, :ref:`Isophotal flux<flux_iso_def>`
_`FLUXERR_ISO`, count, :ref:`RMS error estimate for the isophotal flux<flux_iso_def>`
_`MAG_ISO`, mag, :ref:`Isophotal magnitude<flux_iso_def>`
_`MAGERR_ISO`, mag, :ref:`RMS error estimate for the isophotal magnitude<flux_iso_def>`
_`FLUX_ISOCOR`, count, :ref:`Corrected isophotal flux<mag_isocor_def>`
_`FLUXERR_ISOCOR`, count, :ref:`RMS error estimate for the corrected isophotal flux<mag_isocor_def>`
_`MAG_ISOCOR`, mag, :ref:`Corrected isophotal magnitude<mag_isocor_def>`
_`MAGERR_ISOCOR`, mag, :ref:`RMS error estimate for the corrected isophotal magnitude<mag_isocor_def>`
doc/src/Photom.rst
View file @ e8f9a2ae
.. File Photom.rst
.. include:: global.rst
Photometry
==========
Besides PSF and model-fitting flux estimates, |SExtractor| can currently
perform four types of flux measurements: isophotal, *corrected-isophotal*,
fixed-aperture and *adaptive-aperture*. For every ``FLUX`` measurement,
an error estimate ``FLUXERR``, a magnitude ``MAG`` and a magnitude
error estimate ``MAGERR`` are also available.
Besides PSF and model-fitting flux estimates, |SExtractor| can currently perform four types of flux measurements: isophotal, *corrected-isophotal*, fixed-aperture and *adaptive-aperture*.
For every :param:`FLUX_` measurement, an error estimate :param:`FLUXERR_`, a magnitude :param:`MAG_` and a magnitude error estimate :param:`MAGERR_` are also available.
The ``MAG_ZEROPOINT`` configuration parameter sets the magnitude zero-point
of magnitudes:
......@@ -23,15 +22,12 @@ Magnitude uncertainties (error estimates) are computed using
{\tt MAGERR} = \frac{2.5}{\ln 10}\frac{\tt FLUXERR}{\tt FLUX}
.. _FLUX_ISO:
.. _flux_iso_def:
Isophotal flux
--------------
``FLUX_ISO`` is computed simply by integrating pixels values within the
detection footprint, with the additional constraint that the
background-subtracted, filtered value of detection image pixels must exceed
the threshold set with the ``ANALYSIS_THRESH`` configuration parameter.
:param:`FLUX_ISO` is computed simply by integrating pixels values within the detection footprint, with the additional constraint that the background-subtracted, filtered value of detection image pixels must exceed the threshold set with the ``ANALYSIS_THRESH`` configuration parameter.
.. math::
:label: fluxiso
......@@ -39,27 +35,22 @@ the threshold set with the ``ANALYSIS_THRESH`` configuration parameter.
{\tt FLUX\_ISO} = \sum_{i \in {\cal S}} I_i
Corrected isophotal magnitudes
------------------------------
.. _mag_isocor_def:
Corrected isophotal magnitude
-----------------------------
``MAG_ISOCOR`` can be considered as a quick-and-dirty way for retrieving
the fraction of flux lost by isophotal magnitudes. Although their use is
now deprecated, they have been kept in |SExtractor| v2.x and above for
compatibility with |SExtractor| v1. If we make the assumption that the
intensity profiles of the faint objects recorded in the frame are
roughly Gaussian because of atmospheric blurring, then the fraction
:math:`\eta = \frac{I_{\rm iso}}{I_{\rm tot}}` of the total flux enclosed
within a particular isophote reads :cite:`1990MNRAS_246_433M`:
:param:`MAG_ISOCOR` can be considered as a quick-and-dirty way for retrieving the fraction of flux lost by isophotal magnitudes.
Although their use is now deprecated, they have been kept in |SExtractor| v2.x and above for compatibility with |SExtractor| v1.
If we make the assumption that the intensity profiles of the faint objects recorded in the frame are roughly Gaussian because of atmospheric blurring, then the fraction :math:`\eta = \frac{I_{\rm iso}}{I_{\rm tot}}` of the total flux enclosed within a particular isophote reads :cite:`1990MNRAS_246_433M`:
.. math::
:label: isocor
\left(1-\frac{1}{\eta}\right ) \ln (1-\eta) = \frac{A\,t}{I_{\rm iso}}
where :math:`A` is the area and :math:`t` the threshold related to this
isophote. :eq:isocor is not analytically invertible, but a good
approximation to :math:`\eta` (error :math:`< 10^{-2}` for :math:`\eta >
0.4`) can be done with the second-order polynomial fit:
where :math:`A` is the area and :math:`t` the threshold related to this isophote.
:eq:isocor is not analytically invertible, but a good approximation to :math:`\eta` (error :math:`< 10^{-2}` for :math:`\eta > 0.4`) can be done with the second-order polynomial fit:
.. math::
:label: isocor2
......@@ -67,60 +58,48 @@ approximation to :math:`\eta` (error :math:`< 10^{-2}` for :math:`\eta >
\eta \approx 1 - 0.1961 \frac{A\,t}{I_{\rm iso}} - 0.7512
\left( \frac{A\,t}{I_{\rm iso}}\right)^2 \label{eq:isocor}
A “total” magnitude ``MAG_ISOCOR`` estimate is then
A “total” magnitude :param:`MAG_ISOCOR` estimate is then
.. math::
:label: magisocor
{\tt MAG\_ISOCOR} = {\tt MAG\_ISO} + 2.5 \log_{10} \eta
Clearly this cheap correction works best with stars; and although it is
shown to give tolerably accurate results with most disk galaxies, it
fails with ellipticals because of the broader wings of their profiles.
Clearly this cheap correction works best with stars; and although it is shown to give tolerably accurate results with most disk galaxies, it fails with ellipticals because of the broader wings of their profiles.
.. flux_aper_def:
Fixed-aperture flux
-------------------
``FLUX_APER`` estimates the flux above the background within a circular
:param:`FLUX_APER` estimates the flux above the background within a circular
aperture. The diameter of the aperture in pixels is defined by the
``PHOTOM_APERTURES`` configuration parameter. It does not have to be an
integer: each “normal” pixel is subdivided in :math:`5\times 5` sub-pixels
before measuring the flux within the aperture. If ``FLUX_APER`` is provided as a
vector ``FLUX_APER[n]``, at least :math:`n` apertures must be
before measuring the flux within the aperture. If :param:`FLUX_APER` is provided as a
vector :param:`FLUX_APER[n]`, at least :math:`n` apertures must be
specified with ``PHOTOM_APERTURES``.
Automatic aperture magnitudes
-----------------------------
(MAG\_AUTO) provides an estimate of the “total magnitude” by integrating
the source flux within an adaptively scaled aperture. SExtractor’s
automatic aperture photometry routine is inspired by Kron’s “first
moment” algorithm (1980). (1) We define an elliptical aperture whose
elongation :math:`\epsilon` and position angle :math:`\theta` are
defined by second order moments of the object’s light distribution. The
ellipse is scaled to :math:`R_{\rm max}.\sigma_{\rm iso}`
:param:`MAG_AUTO` provides an estimate of the “total magnitude” by integrating the source flux within an adaptively scaled aperture.
|SExtractor|’s automatic aperture photometry routine is inspired by Kron’s “first moment” algorithm :cite:`1980ApJS_43_305K`.
#. An elliptical aperture is defined whose elongation :math:`\epsilon` and position angle :math:`\theta` are defined by second order moments of the object’s light distribution. The ellipse is scaled to :math:`R_{\rm max}.\sigma_{\rm iso}`
(:math:`6 \sigma_{\rm iso}`, which corresponds roughly to 2 isophotal
“radii”). (2) Within this aperture we compute the “first moment”:
“radii”).
#. Within this aperture the “first moment” is computed:
.. math:: r_1 = \frac{\sum r\,I(r)}{\sum I(r)}
Kron (1980) and Infante (1987) have shown that for stars and galaxy
profiles convolved with Gaussian seeing, :math:`\ge 90\%` of the flux is
expected to lie within a circular aperture of radius :math:`k r_1` if
:math:`k =
2`, almost independently of their magnitude. This picture remains
unchanged if we consider an ellipse with :math:`\epsilon\, k r_1` and
:math:`k r_1 /
\epsilon` as principal axes. :math:`k = 2` defines a sort of balance
between systematic and random errors. By choosing a larger
:math:`k = 2.5`, the mean fraction of flux lost drops from about 10% to
6%. When Signal to Noise is low, it may appear that an erroneously small
aperture is taken by the algorithm. That’s why we have to bound the
smallest accessible aperture to :math:`R_{\rm min}` (typically
:math:`R_{\rm min} = 3 - 4\,
\sigma_{\rm iso}`). The user has full control over the parameters
:math:`k` and :math:`R_{\rm min}` through the configuration parameters
PHOT\_AUTOPARAMS; by default, PHOT\_AUTOPARAMS is set to 2.5,3.5.
:cite:`1980ApJS_43_305K` and :cite:`1987AA_183_177I` have shown that for stars and galaxy profiles convolved with Gaussian seeing, :math:`\ge 90\%` of the flux is expected to lie within a circular aperture of radius :math:`k r_1` if :math:`k = 2`, almost independently of their magnitude.
This picture remains unchanged if one considers an ellipse with :math:`\epsilon\, k r_1` and :math:`k r_1 / \epsilon` as principal axes.
:math:`k = 2` defines a sort of balance between systematic and random errors.
By choosing a larger :math:`k = 2.5`, the mean fraction of flux lost drops from about 10% to 6%.
When Signal to Noise is low, it may appear that an erroneously small aperture is taken by the algorithm.
That’s why we have to bound the smallest accessible aperture to :math:`R_{\rm min}` (typically :math:`R_{\rm min} = 3 - 4\,\sigma_{\rm iso}`).
The user has full control over the parameters :math:`k` and :math:`R_{\rm min}` through the configuration parameters ``PHOT_AUTOPARAMS``; by default, ``PHOT_AUTOPARAMS`` is set to ``2.5,3.5``.
.. figure:: ps/simlostflux.ps
:alt: Flux lost (expressed as a mean magnitude difference) with different faint-object photometry techniques as a function of total magnitude (see text). Only isolated galaxies (no blends) of the simulations have been considered.
......@@ -131,61 +110,40 @@ PHOT\_AUTOPARAMS; by default, PHOT\_AUTOPARAMS is set to 2.5,3.5.
(see text). Only isolated galaxies (no blends) of the simulations
have been considered.
Aperture magnitudes are sensitive to crowding. In SExtractor 1,
MAG\_AUTO measurements were not very robust in that respect. It was
therefore suggested to replace the aperture magnitude by the
corrected-isophotal one when an object is too close to its neighbours (2
isophotal radii for instance). This was done automatically when using
the MAG\_BEST magnitude: :math:`{\tt MAG\_BEST} = {\tt MAG\_AUTO}` when
it is sure that no neighbour can bias MAG\_AUTO by more than 10%, or
:math:`{\tt MAG\_BEST} = {\tt MAG\_ISOCOR}` otherwise. Experience showed
that the MAG\_ISOCOR and MAG\_AUTO magnitude would loose about the same
fraction of flux on stars or compact galaxy profiles: around 0.06 % for
default extraction parameters. The use of MAG\_BEST is now deprecated as
MAG\_AUTO measurements are much more robust in versions 2.x of
SExtractor. The first improvement is a crude subtraction of all the
neighbours which have been detected around the measured source (the
MASK\_TYPE BLANK option). The second improvement is an automatic
correction of parts of the aperture that are suspected to be
contaminated by a neighbour. This is done by mirroring the opposite,
cleaner side of the measurement ellipse if available (the MASK\_TYPE
CORRECT option, which is also the default). Figure [figphot] shows the
mean loss of flux measured with isophotal (threshold
:math:`= 24.4\ \mbox{\rm magnitude\,arsec}^{-2}`), corrected isophotal
and automatic aperture photometries for simulated galaxy :math:`B_J` on
a typical Schmidt-survey plate image. The automatic adaptive aperture
photometry leads to the lowest loss of flux.
Aperture magnitudes are sensitive to crowding.
In |SExtractor| v1, :param:`MAG_AUTO` measurements were not very robust in that respect.
It was therefore suggested to replace the aperture magnitude by the corrected-isophotal one when an object is too close to its neighbors (2 isophotal radii for instance).
This was done automatically when using the :param:`MAG_BEST` magnitude: :math:`{\tt MAG\_BEST} = {\tt MAG\_AUTO}` when it is sure that no neighbor can bias :param:`MAG_AUTO` by more than 10%, and :math:`{\tt MAG\_BEST} = {\tt MAG\_ISOCOR}` otherwise.
Experience showed that the :param:`MAG_ISOCOR` and :param:`MAG_AUTO` magnitude would loose about the same fraction of flux on stars or compact galaxy profiles: around 0.06 % for default extraction parameters.
The use of :param:`MAG_BEST` is now deprecated as :param:`MAG_AUTO` measurements are much more robust in versions 2.x of |SExtractor|.
The first improvement is a crude subtraction of all the neighbors that have been detected around the measured source (``MASK_TYPE BLANK`` option).
The second improvement is an automatic correction of parts of the aperture that are suspected to be contaminated by a neighbor.
This is done by mirroring the opposite, cleaner side of the measurement ellipse if available (``MASK_TYPE CORRECT`` option, which is also the default).
Figure [figphot] shows the mean loss of flux measured with isophotal (threshold :math:`= 24.4\ \mbox{\rm magnitude\,arsec}^{-2}`), corrected isophotal and automatic aperture photometries for simulated galaxy :math:`B_J` on a typical Schmidt-survey plate image.
The automatic adaptive aperture photometry leads to the lowest loss of flux.
Photographic photometry
-----------------------
In DETECT\_TYPE PHOTO mode, SExtractor assumes that the response of the
detector, over the dynamic range of the image, is logarithmic. This is
generally a good approximation for photographic density on deep
exposures. Photometric procedures described above remain unchanged,
except that for each pixel we apply first the transformation
In ``DETECT_TYPE PHOTO`` mode, SExtractor assumes that the response of the detector, over the dynamic range of the image, is logarithmic.
This is generally a good approximation for photographic density on deep exposures.
Photometric procedures described above remain unchanged, except that for each pixel we apply first the transformation
.. math::
I = I_0\,10^{D/\gamma} \ ,
\label{eq:dtoi}
where :math:`\gamma` (MAG\_GAMMA) is the contrast index of the
emulsion, :math:`D` the original pixel value from the
background-subtracted image, and :math:`I_0` is computed from the
magnitude zero-point :math:`m_0`:
where :math:`\gamma` (``MAG_GAMMA``) is the contrast index of the emulsion, :math:`D` the original pixel value from the background-subtracted image, and :math:`I_0` is computed from the magnitude zero-point :math:`m_0`:
.. math:: I_0 = \frac{\gamma}{\ln 10} \,10^{-0.4\, m_0} \ .
One advantage of using a density-to-intensity transformation relative
to the local sky background is that it corrects (to some extent)
large-scale inhomogeneities in sensitivity (see Bertin 1996 for
details).
One advantage of using a density-to-intensity transformation relative to the local sky background is that it corrects (to some extent) large-scale inhomogeneities in sensitivity (see :cite:`1996PhDT_68B` for details).
Errors on magnitude
-------------------
Magnitude uncertainties
-----------------------
An estimate of the error [1]_ is available for each type of magnitude.
An estimate of the error [#error]_ is available for each type of magnitude.
It is computed through
.. math:: \Delta m = 1.0857\, \frac{\sqrt{A\,\sigma^2 + F/g}}{F}
......@@ -193,14 +151,11 @@ It is computed through
where :math:`A` is the area (in pixels) over which the total flux
:math:`F` (in ADU) is summed, :math:`\sigma` the standard deviation of
noise (in ADU) estimated from the background, and g the detector gain
(GAIN parameter [2]_ , in :math:`e^- / \mbox{ADU}`). For
corrected-isophotal magnitudes, a term, derived from Eq. [eq:isocor] is
quadratically added to take into account the error on the correction
itself.
(GAIN parameter [#gain]_ , in :math:`e^- / \mbox{ADU}`).
For corrected-isophotal magnitudes, a term, derived from Eq. [eq:isocor] is quadratically added to take into account the error on the correction itself.
In DETECT\_TYPE PHOTO mode, things are slightly more complex. Making the
assumption that plate-noise is the major contributor to photometric
errors, and that it is roughly constant in density, we can write:
In ``DETECT_TYPE PHOTO`` mode, things are slightly more complex.
Making the assumption that plate-noise is the major contributor to photometric errors, and that it is roughly constant in density, one can write:
.. math::
......@@ -210,31 +165,23 @@ errors, and that it is roughly constant in density, we can write:
\frac{\sqrt{\sum_{x,y}{I^2(x,y)}}}{\sum_{x,y}I(x,y)}
where :math:`I(x,y)` is the contribution of pixel :math:`(x,y)` to the
total flux (Eq. [eq:dtoi]). The GAIN is ignored in PHOTO mode.
total flux (Eq. [eq:dtoi]). ``GAIN`` is ignored in ``PHOTO`` mode.
Background
----------
is the last point relative to photometry. The assumption made in
§[chap:backest] — that the “local” background associated to an object
can be interpolated from the global background map — is no longer valid
in crowded regions. An example is a globular cluster superimposed on a
bulge of galaxy. SExtractor offers the possibility to estimate locally
the background used to compute magnitudes. When this option is switched
on (BACKPHOTO\_TYPE LOCAL instead of GLOBAL), the “photometric”
background is estimated within a “rectangular annulus” around the
isophotal limits of the object. The thickness of the annulus (in pixels)
can be specified by the user with BACKPHOTO\_SIZE. A typical value is
BACKPHOTO\_SIZE=24.
.. [1]
Background is the last point relative to photometry. The assumption made in §[chap:backest] — that the "local" background associated to an object can be interpolated from the global background map — is no longer valid in crowded regions.
An example is a globular cluster superimposed to a bulge of galaxy.
SExtractor offers the possibility to estimate locally the background used to compute magnitudes.
When this option is switched on (``BACKPHOTO_TYPE LOCAL`` instead of ``GLOBAL``), the "photometric" background is estimated within a "rectangular annulus" around the isophotal limits of the object.
The thickness of the annulus (in pixels) can be specified by the user with ``BACKPHOTO_SIZE``. A typical value is ``BACKPHOTO_SIZE``=``24``.
.. [#error]
It is important to note that this error provides a lower limit, since
it does not take into account the (complex) uncertainty on the local
background estimate.
.. [2]
.. [#gain]
Setting GAIN to 0 in the configuration file is equivalent to
:math:`g = +\infty`
.. include:: keys.rst
doc/src/conf.py
View file @ e8f9a2ae
......@@ -90,7 +90,7 @@ today = 'Wed Nov 22 2017'
# List of patterns, relative to source directory, that match files and
# directories to ignore when looking for source files.
# This patterns also effect to html_static_path and html_extra_path
exclude_patterns = ['keys.rst']
exclude_patterns = ['global.rst','keys.rst','roles.rst']
# The reST default role (used for this markup: `text`) to use for all
# documents.
......
doc/src/conf.py.in
View file @ e8f9a2ae
......@@ -90,7 +90,7 @@ today = '@DATE2@'
# List of patterns, relative to source directory, that match files and
# directories to ignore when looking for source files.
# This patterns also effect to html_static_path and html_extra_path
exclude_patterns = ['keys.rst']
exclude_patterns = ['global.rst','keys.rst','roles.rst']
# The reST default role (used for this markup: `text`) to use for all
# documents.
......
doc/src/references.bib
View file @ e8f9a2ae
......@@ -15,7 +15,7 @@
@ARTICLE{2002AA_395_1077C,
author = {{Calabretta}, M.~R. and {Greisen}, E.~W.},
title = "{Representations of celestial coordinates in FITS}",
journal = {A\&A},
journal = {A&A},
eprint = {astro-ph/0207413},
keywords = {methods: data analysis, techniques: image processing, astronomical data bases: miscellaneous, astrometry},
year = 2002,
......@@ -30,7 +30,7 @@
@ARTICLE{2002AA_395_1061G,
author = {{Greisen}, E.~W. and {Calabretta}, M.~R.},
title = "{Representations of world coordinates in FITS}",
journal = {A\&A},
journal = {A&A},
eprint = {astro-ph/0207407},
keywords = {methods: data analysis, techniques: image processing, astronomical data bases: miscellaneous},
year = 2002,
......@@ -42,11 +42,37 @@
adsnote = {Provided by the SAO/NASA Astrophysics Data System}
}
@ARTICLE{1987AA_183_177I,
author = {{Infante}, L.},
title = "{A faint object processing software - Description and testing}",
journal = {A&A},
keywords = {Astronomical Photography, Computer Programs, Computerized Simulation, Faint Objects, Image Processing, Algorithms, Astronomical Photometry, Galaxies, Red Shift, Stars},
year = 1987,
month = sep,
volume = 183,
pages = {177-184},
adsurl = {http://adsabs.harvard.edu/abs/1987A&A...183..177I},
adsnote = {Provided by the SAO/NASA Astrophysics Data System}
}
@ARTICLE{1980ApJS_43_305K,
author = {{Kron}, R.~G.},
title = "{Photometry of a complete sample of faint galaxies}",
journal = {ApJS},
keywords = {Astronomical Photometry, Galactic Radiation, Galaxies, Star Distribution, Calibrating, Colorimetry, Distribution Functions, Galactic Evolution, Luminous Intensity, Tables (Data)},
year = 1980,
month = jun,
volume = 43,
pages = {305-325},
doi = {10.1086/190669},
adsurl = {http://adsabs.harvard.edu/abs/1980ApJS...43..305K},
adsnote = {Provided by the SAO/NASA Astrophysics Data System}
}
@ARTICLE{1990MNRAS_246_433M,
author = {{Maddox}, S.~J. and {Efstathiou}, G. and {Sutherland}, W.~J.
},
author = {{Maddox}, S.~J. and {Efstathiou}, G. and {Sutherland}, W.~J.},
title = "{The APM Galaxy Survey - Part Two - Photometric Corrections}",
journal = {\mnras},
journal = {MNRAS},
year = 1990,
month = oct,
volume = 246,
......@@ -57,8 +83,7 @@
@ARTICLE{1856MNRAS_17_12P,
author = {{Pogson}, N.},
title = "{Magnitudes of Thirty-six of the Minor Planets for the first day of each month
of the year 1857}",
title = "{Magnitudes of Thirty-six of the Minor Planets for the first day of each month of the year 1857}",
journal = {MNRAS},
year = 1856,
month = nov,
......@@ -128,4 +153,14 @@ booktitle = {Conference on Applications of Digital Image Processing to Astronomy
adsnote = {Provided by the SAO/NASA Astrophysics Data System}
}
@PHDTHESIS{1996PhDT_68B,
author = {{Bertin}, E.},
title = "{Photom\'etrie automatique de galaxies et contraintes sur leur \'evolution r\'ecente}",
school = {PhD Thesis.~Universit{\'e} Paris VI., (1996)},
year = 1996,
month = jun,
adsurl = {http://adsabs.harvard.edu/abs/1996PhDT........68B},
adsnote = {Provided by the SAO/NASA Astrophysics Data System}
}
doc/theme/css/custom.css
View file @ e8f9a2ae
......@@ -11,6 +11,7 @@ h1,h2,h3 {
font-weight: 700;
src: url(../fonts/CherrySoda.ttf) format('truetype');
}
*/
/* Extend page width size limit */
.wy-nav-content {
......@@ -71,3 +72,14 @@ span[id*="MathJax-Span"] {
visibility: visible;
}
/* new param class */
@font-face {
font-family: MathJax_Typewriter;
src: url('https://cdnjs.cloudflare.com/ajax/libs/mathjax/2.7.1/fonts/HTML-CSS/TeX/woff/MathJax_Typewriter-Regular.woff?V=2.7.1') format('woff'), url('https://cdnjs.cloudflare.com/ajax/libs/mathjax/2.7.1/fonts/HTML-CSS/TeX/otf/MathJax_Typewriter-Regular.otf?V=2.7.1') format('opentype')
}
.targetparam .target, .param {
font-family: "MathJax_Typewriter",monospace;
font-size: 116%;
}
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