Changeset 25908

Timestamp:

Oct 21, 2009, 12:43:41 PM (17 years ago)

Author:

eugene

Message:

correctly handle cases of per-exposure vs per-chip zero point stats

Location:

trunk/Ohana/src/addstar/src

Files:

• GetZeroPointExposure.c (modified) (4 diffs)
• ReadImageHeader.c (modified) (2 diffs)

trunk/Ohana/src/addstar/src/GetZeroPointExposure.c

@@ -1 +1 @@
 # include "addstar.h"
 
-// XXX this needs to handle the nominal zero point for the photcode(s) and the airmass term
+// this function evaluates the collection of image headers for keywords of the form ZPT_OBS.
+// Downstream, we will set the zero point offset for the image (image[0].Mcal) based on the
+// value calculated here and the nominal zero point for the chip photcode. Four possible modes
+// are defined: 
+
+// NOMINAL: in this case, the database value for the nominal zero point is used and
+// image[0].Mcal is set to zero.
+
+// CHIP_HEADER: in this case, the zero point offset measured for each chip is applied
+// independently to image[0].Mcal
+
+// CHIP_AVERAGE: in this case, the per-chip measured zero points are converted to offsets from
+// the nominal zero points, and the median zero point offset is calculate, and later applied to
+// image[0].Mcal
+
+// PHU_HEADER: in this case, the zero point measured for the entire exposure and reported in
+// the PHU header is used to set the zero point offset for each chip.  Note that in this case,
+// ZERO_POINT_OFFSET in this funciton is actually set to the zero point, and adjusted to an
+// offset in ReadImageHeader based on the per-chip zero points in the photcode database
+
 int GetZeroPointExposure (Header **headers, HeaderSet *headerSets, int Nimages) {
 
+    // the zero point correction is not applied
     if (!strcasecmp(ZERO_POINT_OPTION, "NOMINAL")) {
         ZERO_POINT_OFFSET = 0.0;
@@ -9 +29 @@
     }
 
+    // the zero point correction is applied in ReadImageHeader
     if (!strcasecmp(ZERO_POINT_OPTION, "CHIP_HEADER")) {
         ZERO_POINT_OFFSET = 0.0;
@@ -14 +35 @@
     }
 
+    // the zero point correction is measured here and applied in ReadImageHeader
     if (!strcasecmp(ZERO_POINT_OPTION, "CHIP_AVERAGE")) {
         int i, Nzpt, Nmid, Nhead;
@@ -66 +88 @@
     }
     
-    // this option is not consistent with the options for photcodes
+    // the zero point (NOT the correction) is measured here and applied in ReadImageHeader
     if (!strcasecmp(ZERO_POINT_OPTION, "PHU_HEADER")) {
         int i, Nhead;

trunk/Ohana/src/addstar/src/ReadImageHeader.c

@@ -203 +203 @@
   }
 
-  // if it exists, find the 
+  // in this case, lookup and apply the zero point measured for this chip
   if (!strcasecmp(ZERO_POINT_OPTION, "CHIP_HEADER")) {
       float ZPT_OBS;
@@ -214 +214 @@
   }
 
+  // in this case, lookup and apply the zero point measured for the exposure
+  if (!strcasecmp(ZERO_POINT_OPTION, "PHU_HEADER")) {
+      if (!photcodeData) {
+          fprintf (stderr, "photcode data not supplied for this chip\n");
+          ZERO_POINT_OFFSET = 0.0;
+      } else {
+          ZERO_POINT_OFFSET = 0.001*photcodeData[0].C - ZERO_POINT_OFFSET;
+      }   
+  }
+
   /* secz is in units milli-airmass */
   image[0].Mcal = ZERO_POINT_OFFSET;