Index: /trunk/psastro/src/psastroChooseRefstars.c
===================================================================
--- /trunk/psastro/src/psastroChooseRefstars.c	(revision 19031)
+++ /trunk/psastro/src/psastroChooseRefstars.c	(revision 19032)
@@ -62,9 +62,12 @@
                 if (! readout->data_exists) { continue; }
 
-                // read WCS data from the corresponding header
-                pmHDU *hdu = pmFPAviewThisHDU (view, fpa);
+		psRegion *extent = pmReadoutExtent (readout);
+		if (!extent) {
+		    psError(PSASTRO_ERR_CONFIG, true, "Can't find readout size!\n");
+		    return NULL;
+		}
 
-                int Nx = psMetadataLookupS32 (&status, hdu->header, "NAXIS1");
-                int Ny = psMetadataLookupS32 (&status, hdu->header, "NAXIS2");
+		int Nx = abs(extent->x1 - extent->x0);
+		int Ny = abs(extent->y1 - extent->y0);
 
                 float minX = -fieldPadding*Nx;
@@ -101,4 +104,5 @@
 		psMetadataAdd (readout->analysis, PS_LIST_TAIL, "PSASTRO.REFSTARS", PS_DATA_ARRAY, "astrometry matches", refstars);
 		psFree (refstars);
+		psFree (extent);
 
 		if (matchLumFunc) {