Changes between Version 62 and Version 63 of Sa10Problems

Timestamp:

Dec 13, 2012, 1:39:50 PM (14 years ago)

Author:

eugene

Comment:

--

Sa10Problems

@@ -79 +79 @@
      *  a. '''EAM : x & y position error are actually based on the fwhmMajor and fwhmMinor values and the S/N: x = fwhmMajor / (S/N * 2.35), y = fwhmMinor / (S/N * 2.35).  these are reasonable (but note the angle compared to the x,y axis), but go to interesting values for very low S/N objects or those with negative fluxes.  perhaps it should saturate at 0.5*ap_radius_raw?'''
     * 5. raerr & decerr: quantized in 0.25 steps + in silly units  (not the same as xposerr)+ negative from time to time (not just -999)  + range is huge (-8000 to 8000)
-      * a. '''gene to investigate - note that ra/dec err are in units of arcsecond '''
+      * a. '''EAM : these come from (dXccd,dYccd)*pltscale.  five points to be made: 
+        * i. ra/dec err are (supposed to be) in units of arcsecond
+        * ii. pltscale can be negative : negative value means the image has the opposite of sky parity.  the code should use abs(pltscale)
+        * iii. dXccd,dYccd are in units of 1/100th of a pixel in DVO, so there is a factor of 100 error in the conversion
+        * iv. dXccd,dYccd are stored in DVO as a short, so are quantized at the 10 millipixel level (but this should not be a problem)
+        * v. dXccd,dYccd are measured from the fwhm and S/N as described above, so the same blowup at the faint end occurs'''
     * 6. apFluxerr: -999 (i.e. never set)
       *  a. '''noted before on previous SASs. not to be fixed yet'''