ELLMAG: Compute Elliptical Magnitudes for PROFILE Ellipses

ELLMAG calculates the elliptical magnitude within the elliptical isophote fit using the PROFILE command. It uses the values for the surface brightness computed previously by PROFILE. It recomputes the circular totals using CIRCMAG, so that any results appended to the PROFILE results with EMAG will have appropriate circular totals all the way out to the final radius.

This routine differs from EMAG in that the magnitudes within each ellipse in the PROFILE common block are computed, correctly taking into account the varying position angles and eccentricities. EMAG, by contrast, computes concentric elliptical magnitudes given the parameters for ONE of the ellipses in the PROFILE common block.

This routine uses the SB results to approximate the elliptical totals within increasing semi-major axis radii. For each increase in radius, the routine approximates the additional ellipse area which needs to be taken into account for calculating the elliptical totals. It then multiplies the SB value at that radius by this area to get an approximation of the extra number of counts to add to the elliptical total. The routine does take into account the possibility of crossing ellipses but, at this time, does not yet take into account the possibility of changing position angle.