Index: trunk/psModules/src/camera/pmFPAExtent.c
===================================================================
--- trunk/psModules/src/camera/pmFPAExtent.c	(revision 11124)
+++ trunk/psModules/src/camera/pmFPAExtent.c	(revision 12520)
@@ -4,4 +4,5 @@
 #include "pmFPA.h"
 
+// return cell pixels bounding the readout
 psRegion *pmReadoutExtent(const pmReadout *readout)
 {
@@ -30,5 +31,5 @@
 }
 
-
+// return chip pixels bounding the cell (all readouts)
 psRegion *pmCellExtent(const pmCell *cell)
 {
@@ -69,10 +70,10 @@
 }
 
-
-psRegion *pmChipExtent(const pmChip *chip)
+// return chip pixels included in all cells
+psRegion *pmChipPixels(const pmChip *chip)
 {
     PS_ASSERT_PTR_NON_NULL(chip, NULL);
 
-    psArray *cells = chip->cells;       // Arrya of component cells
+    psArray *cells = chip->cells;       // Array of component cells
     psRegion *chipExtent = psRegionAlloc(INFINITY, 0, INFINITY, 0); // Extent of chip
     for (long i = 0; i < cells->n; i++) {
@@ -85,4 +86,17 @@
         psFree(cellExtent);
     }
+
+    return chipExtent;
+}
+
+// return pixels in basic FPA grid bounded by chip
+// this FPA grid has 0,0 at the 0,0 corner of one chip, and is NOT the same
+// as the astrometry focal plane coordinate system
+psRegion *pmChipExtent(const pmChip *chip)
+{
+    PS_ASSERT_PTR_NON_NULL(chip, NULL);
+
+    psRegion *chipExtent = pmChipPixels(chip);
+    if (!chipExtent) return NULL;
 
     bool mdok;                          // Status of MD lookup
@@ -108,10 +122,12 @@
 }
 
-
-psRegion *pmFPAExtent(const pmFPA *fpa)
+// return FPA pixels included in all chips
+// this FPA grid has 0,0 at the 0,0 corner of one chip, and is NOT the same
+// as the astrometry focal plane coordinate system
+psRegion *pmFPAPixels(const pmFPA *fpa)
 {
     PS_ASSERT_PTR_NON_NULL(fpa, NULL);
 
-    psArray *chips = fpa->chips;       // Arrya of component chips
+    psArray *chips = fpa->chips;       // Array of component chips
     psRegion *fpaExtent = psRegionAlloc(INFINITY, 0, INFINITY, 0); // Extent of fpa
     for (long i = 0; i < chips->n; i++) {