Index: trunk/psastro/src/psastroAstromGuess.c
===================================================================
--- trunk/psastro/src/psastroAstromGuess.c	(revision 12492)
+++ trunk/psastro/src/psastroAstromGuess.c	(revision 12536)
@@ -47,4 +47,17 @@
     pmFPA *fpa = input->fpa;
 
+    // load mosaic-level astrometry?
+    bool bilevelAstrometry = false;
+    pmHDU *phu = pmFPAviewThisPHU (view, fpa);
+    if (phu) {
+      char *ctype = psMetadataLookupStr (NULL, phu->header, "CTYPE1");
+      if (ctype) {
+	bilevelAstrometry = !strcmp (&ctype[4], "-DIS");
+      }
+    }
+    if (bilevelAstrometry) {
+      pmAstromReadBilevelMosaic (fpa, phu->header);
+    } 
+
     while ((chip = pmFPAviewNextChip (view, fpa, 1)) != NULL) {
         psTrace ("psastro", 4, "Chip %d: %x %x\n", view->chip, chip->file_exists, chip->process);
@@ -53,6 +66,10 @@
         // read WCS data from the corresponding header
         pmHDU *hdu = pmFPAviewThisHDU (view, fpa);
+	if (bilevelAstrometry) {
+	  pmAstromReadBilevelChip (chip, hdu->header); 
+	} else {
+	  pmAstromReadWCS (fpa, chip, hdu->header, pixelScale);
+	}
 
-        pmAstromReadWCS (fpa, chip, hdu->header, pixelScale);
         if (newFPA) {
             newFPA = false;