Changeset 15802

Timestamp:

Dec 12, 2007, 6:07:17 PM (18 years ago)

Author:

eugene

Message:

change psfProb to psfChisq

File:

• trunk/psphot/src/psphotSourceSize.c (modified) (2 diffs)

trunk/psphot/src/psphotSourceSize.c

@@ -53 +53 @@
         float nR = cR / sqrt(dcR);
 
-        float chisq = PS_SQR (nX) + PS_SQR (nY) + PS_SQR (nX) + PS_SQR (nR);
-
         // P(chisq > chisq_obs; Ndof) = gamma_Q (Ndof/2, chisq/2)
         // Ndof = 4 ? (four measurements, no free parameters)
         // XXX this value is going to be biased low because of systematic errors.
         // we need to calibrate it somehow
-        source->psfProb = gsl_sf_gamma_inc_Q (2, 0.5*chisq);
+        // source->psfProb = gsl_sf_gamma_inc_Q (2, 0.5*chisq);
+
+        // not strictly accurate: overcounts the chisq contribution from the center pixel (by factor of 4)
+        source->psfChisq = PS_SQR (nX) + PS_SQR (nY) + PS_SQR (nX) + PS_SQR (nR);
 
         float fCR = 0.0;
@@ -94 +95 @@
         }
         source->crNsigma  = (nCR > 0)  ? fCR / nCR : 0.0;
-        source->extNsigma = (nEXT > 0) ? fEXT / nEXT : 0.0;
+        source->extNsigma = (nEXT > 0) ? fabs(fEXT) / nEXT : 0.0;
+        // NOTE: abs needed to make the Nsigma value positive 
     }
     return true;