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 position 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 following 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-sec-
onds.
-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