Re: Definition of roundness parameter

Posted by karenacollins on
URL: http://astroimagej.170.s1.nabble.com/Definition-of-roundness-parameter-tp2172p2173.html

The reported values are a relative measurement of the roundness (vs. eccentric due to tracking or guiding problems) of the stellar PSF in the aperture. The measurement is a by-product of the centroiding routine which provides estimates of the FWHM values in both the x-axis and y-axis directions. The roundness is then 1 - ecc, where ecc = ((xWidth-yWidth)*(xWidth-yWidth)+4.0*mxy*mxy)/((xWidth+yWidth)*(xWidth+yWidth)), and where mxy is a representation of the combined FWHM estimate. If you need more detailed information, you'll need to look at the AIJ code in Centroid.java starting at line 540.

Karen