Weighting section translated into sphinx. Some ref to other sections are still missing.

.. File Using.rst

.. _using-sextractor:

Using SExtractor

================

correlations on small scales. This proves to be a good approximation in general, although it certainly leads to

underestimations for the smallest patterns.

.. _weigth-map-format:

Weight-map formats

------------------

or computed internally.

Valid ``WEIGHT_TYPE`` values are:

* ``NONE`` : No weighting is applied. The related ``WEIGHT_IMAGE`` and ``WEIGHT_THRESH`` (see below) parameters are ignored.

* ``NONE`` :

    No weighting is applied. The related ``WEIGHT_IMAGE`` and ``WEIGHT_THRESH`` (see below) parameters are ignored.

* ``BACKGROUND`` : the science image itself is used to compute internally a variance map (the related ``WEIGHT_IMAGE``

* ``BACKGROUND`` :

    the science image itself is used to compute internally a variance map (the related ``WEIGHT_IMAGE``

    parameter is ignored). Robust (:math:`3\sigma`-clipped) variance estimates are first computed within the same

    background meshes as those described in ?? [12] (The mesh-filtering procedures act on the variance map, too.).

    background meshes as those described in ?? [#f1].

    The resulting low-resolution variance map is then bicubic-spline-interpolated on the fly to produce

    the actual full-size variance map.

    A check-image with ``CHECKIMAGE_TYPE`` ``MINIBACK_RMS`` can be requested to examine the low-resolution variance map.

* ``MAP_RMS`` : the FITS image specified by the ``WEIGHT_IMAGE`` file name must contain a weight-map in units of

* ``MAP_RMS`` :

    the FITS image specified by the ``WEIGHT_IMAGE`` file name must contain a weight-map in units of

    absolute standard deviations (in ADUs per pixel).

* ``MAP_VAR`` : the FITS image specified by the ``WEIGHT_IMAGE`` file name must contain a weight-map in units of

* ``MAP_VAR`` :

    the FITS image specified by the ``WEIGHT_IMAGE`` file name must contain a weight-map in units of

    relative variance. A robust scaling to the appropriate absolute level is then performed by comparing this

    variance map to an internal, low-resolution, absolute variance map built from the science image itself.

* ``MAP_WEIGHT`` : the FITS image specified by the ``WEIGHT_IMAGE`` file name must contain a weight-map in units of

* ``MAP_WEIGHT`` :

    the FITS image specified by the ``WEIGHT_IMAGE`` file name must contain a weight-map in units of

    relative weights.

    The data are converted to variance units (by definition variance :math:`\propto\frac{1}{weight}`),

    and scaled as for ``MAP_VAR``.

Combining weight maps

---------------------

All the weighting options listed in ?? can be applied separately to detection and measurement images (??),

even if some combinations may not always make sense.

All the weighting options listed in :ref:`weigth-map-format` can be applied separately to detection and measurement images

(:ref:`using-sextractor`), even if some combinations may not always make sense.

For instance, the following set of configuration lines:

``WEIGHT_IMAGE`` *rms.fits*, *weight.fits*

will load the FITS file *rms.fits* and use it as an RMS map for adjusting the detection threshold and cleaning,

while the *weight.fits* weight map will only be used for scaling the error estimates on measurements.

This can be done in single- as well as in dual-image mode (??).

This can be done in single- as well as in dual-image mode (:ref:`using-sextractor`).

``WEIGHT_IMAGE`` can be ignored for ``BACKGROUND`` ``WEIGHT_TYPE``.

It is of course possible to use weight-maps for detection or for measurement only.

The following configuration:

will apply weighting only for measurements; detection and cleaning operations will remain unaffected.

.. rubric:: Footnotes

.. [#f1] The mesh-filtering procedures act on the variance map, too.

.. include:: keys.rst