... Meta Index / Home Page / Description / Source circle radii. ... For this setting of radiusstyle , the size of each radius is scaled from the brightness of the source. An elliptical locus is obtained at which the source rate per pixel (which is, remember, not truly point-like but spread out over the PSF) decreases to some given fraction of the background rate. ... If withellipse =`yes', this ellipse is drawn, but if withellipse =`no', a circle of radius equal to the larger semi-axis is drawn. ...