Name
encircl - Encircled Energy Computation
Synopsis
encircl [options] <cubes> <parameters>
Description
encircl computes the encircled energy for every plane in a
cube given on command line. See ALGORITHM to know how it
is computed. encircl needs to be given some parameters in
order to work. These parameters are the approximate posi-
tion of the peak on which the user wants to find encircled
energy radius, as well as the percentage of the total
energy for which the radius is wanted.
Algorithm
For each image in each cube (candidate image), the follow-
ing algorithm is applied:
1. Check the validity of the window.
2. Find the position of the pixel of maximum intensity and
re-center the window on that pixel.
3. Calculate the energy encircled in the 100 % radius and
multiply it by the percentage of the total energy for
which the radius is wanted.
4. Calculate the encircled energy for every radius from 1
pixel to the 100 % radius and store the results in an
array.
5. Look up the array to find the two entries whose values
are nearest to that corresponding to the percentage of
interrest of the total energy.
6. Use a linear interpolation to find more precisely what
the radius is.
Options
-p Plate Scale
Plate scale in arc-seconds per pixel, for an output
in arc-seconds.
-r Radius
To override the hard coded size of the 100 % energy
radius (1.4").
-h half-size
To override the default 20 pix value of the window
half size.
Example
To determine the radius for which the encircled energy is
50 % of the total encircled energy for an star whose
energy we know to be located in a window of 42x42 pixels
roughly centered on pixel 60,60 of image star.fits with a
plate scale of 0.1" we want to set the 100 % energy radius
to 1.1" use:
encircl -h 21 -p 0.1 -r 1.1 star.fits 60 60 50
Files
Files shall all comply with FITS format
See Also
stcube, strehl, fwhm