Index: branches/pap/ppSub/src/ppSubReadoutInverse.c
===================================================================
--- branches/pap/ppSub/src/ppSubReadoutInverse.c	(revision 23948)
+++ branches/pap/ppSub/src/ppSubReadoutInverse.c	(revision 25027)
@@ -7,5 +7,4 @@
 
 #include "ppSub.h"
-
 
 bool ppSubReadoutInverse(pmConfig *config)
@@ -24,5 +23,23 @@
     invRO->data_exists = invRO->parent->data_exists = invRO->parent->parent->data_exists = true;
 
-    pmConceptsCopyFPA(invRO->parent->parent->parent, outRO->parent->parent->parent, true, true);
+    // Get concepts from reference
+    pmFPAfile *refFile = psMetadataLookupPtr(NULL, config->files, "PPSUB.REF.CONV"); // File with concepts
+    pmFPA *invFPA = invRO->parent->parent->parent; // Inverse FPA
+    pmConceptsCopyFPA(invFPA, refFile->fpa, true, true);
+
+    // Get astrometry from (forward) subtraction
+    pmChip *outChip = outRO->parent->parent;       // Output chip
+    pmFPA *outFPA = outChip->parent;               // Output FPA
+    pmChip *invChip = invRO->parent->parent; // Inverse chip
+    pmHDU *invHDU = invFPA->hdu;          // Inverse HDU
+    if (!pmAstromWriteWCS(invHDU->header, outFPA, outChip, WCS_TOLERANCE)) {
+        psError(PS_ERR_UNKNOWN, false, "Unable to write WCS astrometry to PPSUB.INVERSE.");
+        return false;
+    }
+    // Read from newly written astrometry so that it exists in the "inverse" FPA (for sources)
+    if (!pmAstromReadWCS(invFPA, invChip, invHDU->header, 1.0)) {
+        psError(PS_ERR_UNKNOWN, false, "Unable to read WCS astrometry.");
+        return false;
+    }
 
     return true;