-- APPHOT Package Update
The following major changes have been made to the aperture photometry
apphot in IRAF V2.10.3BETA.
The apphot tasks
were modified to support the
graphics kernel, used to draw graphics overlays on the image display.
These tasks will mark the positions of detected or selected objects
and draw the sky, photometry, and fitting apertures as appropriate if the
user 1) runs the task in interactive mode, 2) sets the task parameter
display to "imd", and 3) sets the appropriate graphics parameters,
e.g., ``mkcenter'', ``mksky'', and ``mkapert'' to "yes".
The star finding task
and its algorithm parameter
sets have undergone
The datapars parameter ``cthreshold'' has been moved
parameter set and redefined in units
of the datapars parameter ``sigma''
rather than units of counts. Together ``cthreshold'' and ``sigma'' define
the faintest pixels that can be used by the centering algorithms in the
The parameter convolution specifying the name of
the output density enhancement image has been renamed starmap,
and a new parameter specifying the name of the output background
density image skymap has been added. The sum of these two images
models the input image except at the image edges and in regions
containing bad data.
daofind has been modified to read the
``datamin'' and ``datamax''. These parameters are used to
reject bad data from the computed density enhancement and
background density images.
The object detection parameters
``nsigma'', ``ratio'', ``theta'', ``sharplo'', ``sharphi'',
``roundlo'', ``roundhi'', and ``mkdetections'' have been moved to
parameter set task.
The datapars parameter ``threshold'' has been
moved to the findpars parameter set and defined
in units of the datapars
parameter ``sigma'' rather than units of counts. Together
``threshold'' and ``sigma'' set the brightness of the faintest star that
can be detected by the daofind task.
Two new keystroke commands `a' and `o' were added to the
photometry tasks qphot, phot, polyphot,
radprof, and wphot. The `a'
keystroke command computes the sky value by averaging sky values
computed at several cursor positions, and the `o' keystroke command uses
the computed value to do the photometry. The new commands
add an offset sky capability to the apphot photometry
tasks which can be useful
for measuring extended asymmetric objects like comets.
The sky fitting algorithms and associated parameter set
used by the
have undergone major changes.
Two new keystroke commands `m' and `n' have been added to
the apphot tasks.
These commands permit the user to move to the next object in the coordinate
list or measure the next object in the coordinate list, respectively, by
typing a single keystroke rather than the two key-strokes
required by the equivalent `:m' and `:n' commands.
Two new parameters ``sloclip'' and ``shiclip'' have been added
to the fitskypars parameter set. ``sloclip'' and ``shiclip'' define
the percentage of pixels to be clipped from the low and high sides of the
sorted sky pixel distribution after bad data is rejected but before
the sky value is computed by the photometry tasks. Their default values are
0 and 0, respectively.
The fitskypars parameter ``skreject'' specifying
the k-sigma rejection limit
has been replaced with two new parameters, ``sloreject'' and ``shireject'',
specifying the low and high side k-sigma rejection criteria, respectively.
The default value of the fitskypars parameter ``salgorithm'' was changed
from "mode" to "centroid" to minimize sky determination problems for data
taken in regions with very confused background (e.g., nebulosity) and
with data taken where the background noise is poorly sampled.
The definition of the median of the sky pixel distribution was changed
from the average of the central 10 pixels to the average of the central
5% of the pixels. Both definitions were intended to help protect against
quantization effects in the data but the newer definition gives a more
consistent definition and better results.
The bad sky pixel rejection code has been modified to provide better
protection against deviant pixels in the sky distribution.
In the first bad sky pixel rejection cycle, the data is limited
to values between
[sky-min (sky-mindata, maxdata-sky, sloreject*skysigma)] and
[sky + min (sky-mindata, maxdata-sky, shireject*skysigma)] instead
of values between [sky-sloreject*skysigma] and [sky +
as before. This change
provides better protection against deviant pixels in cases where the
user forgets to set ``datamin'' or ``datamax'', and against defects
like cosmic rays which are inside the good data limits but can
sometimes bias the computation of skysigma.
The value of sky in the above expressions is the median of the original sky
pixel distribution except in the case of the "mean" algorithm where it is
the mean or the original distribution.
The size and resolution of the sky pixel histogram required by
the "histplot", "centroid", "gauss", "crosscor", and "ofilt" sky fitting
algorithms is no longer determined by the value of the
parameter ``sigma'' if it is defined.
Instead the computed median and
standard deviation of the sky pixels, the values of the ``khist''
and ``binsize'' parameters, and limits defined by
[median-min (median-mindata, maxdata-median, khist*sigma)]
and [median + max (median-mindata,
maxdata-median, khist*sigma)] are always used to determine the total
width and binwidth of the sky histogram.
Users who have not yet upgraded to IRAF 2.10.3BETA or who are running IRAF on
platforms for which IRAF 2.10.3BETA or a later version is not yet available,
can acquire the updated version of apphot by retrieving and installing
the external package
digiphotx from the IRAF network archive.
This document was translated by ms2html v1.8 on 21Jan95.