Index: trunk/ppSim/src/ppSimMakeSky.c
===================================================================
--- trunk/ppSim/src/ppSimMakeSky.c	(revision 14816)
+++ trunk/ppSim/src/ppSimMakeSky.c	(revision 16497)
@@ -3,4 +3,6 @@
 // XXX add bounds to the inputs?
 bool ppSimMakeSky (pmReadout *readout, psImage *expCorr, ppSimType type, pmConfig *config) {
+
+    bool status;
 
     psImage *signal = readout->image;
@@ -11,19 +13,26 @@
     pmFPA  *fpa  = chip->parent;
 
-    float expTime = psMetadataLookupF32(NULL, config->arguments, "EXPTIME"); // Exposure time
-    float flatSigma = psMetadataLookupF32(NULL, config->arguments, "FLAT.SIGMA"); // Flat-field coefficient
-    float flatRate = psMetadataLookupF32(NULL, config->arguments, "FLAT.RATE"); // Flat-field rate
-    float shutterTime = psMetadataLookupF32(NULL, config->arguments, "SHUTTER.TIME"); // Shutter time
-    float skyRate = psMetadataLookupF32(NULL, config->arguments, "SKY.RATE"); // Sky rate
+    float expTime     = psMetadataLookupF32(&status, config->arguments, "EXPTIME"); // Exposure time
+    float flatSigma   = psMetadataLookupF32(&status, config->arguments, "FLAT.SIGMA"); // Flat-field coefficient
+    float flatRate    = psMetadataLookupF32(&status, config->arguments, "FLAT.RATE"); // Flat-field rate
+    float shutterTime = psMetadataLookupF32(&status, config->arguments, "SHUTTER.TIME"); // Shutter time
 
-    int x0Chip = psMetadataLookupS32(NULL, chip->concepts, "CHIP.X0");
-    int y0Chip = psMetadataLookupS32(NULL, chip->concepts, "CHIP.Y0");
-    int xParityChip = psMetadataLookupS32(NULL, chip->concepts, "CHIP.XPARITY");
-    int yParityChip = psMetadataLookupS32(NULL, chip->concepts, "CHIP.YPARITY");
+    float skyRate     = psMetadataLookupF32(&status, config->arguments, "SKY.RATE"); // Sky rate
+    if (isnan(skyRate)) {
+	float zp      = psMetadataLookupF32(&status, config->arguments, "ZEROPOINT"); assert (status);
+	float scale   = psMetadataLookupF32(&status, config->arguments, "SCALE");     assert (status);
+	float skyMags = psMetadataLookupF32(&status, config->arguments, "SKY.MAGS");  assert (status);
+	skyRate = scale * scale * pow (10.0, -0.4*(skyMags - zp));
+    }
 
-    int x0Cell = psMetadataLookupS32(NULL, cell->concepts, "CELL.X0");
-    int y0Cell = psMetadataLookupS32(NULL, cell->concepts, "CELL.Y0");
-    int xParityCell = psMetadataLookupS32(NULL, cell->concepts, "CELL.XPARITY");
-    int yParityCell = psMetadataLookupS32(NULL, cell->concepts, "CELL.YPARITY");
+    int x0Chip 	      = psMetadataLookupS32(&status, chip->concepts, "CHIP.X0");
+    int y0Chip 	      = psMetadataLookupS32(&status, chip->concepts, "CHIP.Y0");
+    int xParityChip   = psMetadataLookupS32(&status, chip->concepts, "CHIP.XPARITY");
+    int yParityChip   = psMetadataLookupS32(&status, chip->concepts, "CHIP.YPARITY");
+
+    int x0Cell 	      = psMetadataLookupS32(&status, cell->concepts, "CELL.X0");
+    int y0Cell 	      = psMetadataLookupS32(&status, cell->concepts, "CELL.Y0");
+    int xParityCell   = psMetadataLookupS32(&status, cell->concepts, "CELL.XPARITY");
+    int yParityCell   = psMetadataLookupS32(&status, cell->concepts, "CELL.YPARITY");
 
     int binning = psMetadataLookupS32(NULL, config->arguments, "BINNING"); // Binning in x and y