Index: trunk/pswarp/src/pswarpDefine.c
===================================================================
--- trunk/pswarp/src/pswarpDefine.c	(revision 27989)
+++ trunk/pswarp/src/pswarpDefine.c	(revision 34800)
@@ -41,5 +41,5 @@
         return false;
     }
-
+    
     // open the full skycell file; no need to defer different depths. only load the header data
     pmFPAview *view = pmFPAviewAlloc (0);
@@ -86,4 +86,6 @@
         psMetadataItemSupplement(&status, target->concepts, source->concepts, "CELL.X0");
         psMetadataItemSupplement(&status, target->concepts, source->concepts, "CELL.Y0");
+
+	
     }
 
@@ -123,9 +125,153 @@
         }
     }
-
+    
     view->chip = view->cell = view->readout = -1;
     pmFPAAddSourceFromView(output->fpa, view, output->format);
+
 
     psFree (view);
     return true;
 }
+
+bool pswarpDefineBackground (pmConfig *config) {
+
+    // load the PSWARP recipe
+    psMetadata *recipe = psMetadataLookupPtr (NULL, config->recipes, PSWARP_RECIPE);
+    if (!recipe) {
+        psError(PSWARP_ERR_CONFIG, true, "Can't find PSWARP recipe!\n");
+        return false;
+    }
+
+    // select the input data sources
+    pmFPAfile *skycell = psMetadataLookupPtr (NULL, config->files, "PSWARP.SKYCELL");
+    if (!skycell) {
+        psError(PSWARP_ERR_CONFIG, false, "Can't find skycell data!\n");
+        return false;
+    }
+    pmFPAfile *output = psMetadataLookupPtr(NULL, config->files, "PSWARP.OUTPUT.BKGMODEL");
+    if (!output) {
+        psError(PSWARP_ERR_CONFIG, false, "Can't find output data!\n");
+        return false;
+    }
+    pmFPAfile *input = psMetadataLookupPtr(NULL, config->files, "PSWARP.INPUT");
+    if (!input) {
+        psError(PSWARP_ERR_CONFIG, false, "Can't find input data!\n");
+        return false;
+    }
+    
+    // open the full skycell file; no need to defer different depths. only load the header data
+    pmFPAview *view = pmFPAviewAlloc (0);
+    pmFPAfileOpen (skycell, view, config);
+
+    // Read header and create target
+    {
+        if (!pmFPAReadHeaderSet(skycell->fpa, skycell->fits, config)) {
+            psError(psErrorCodeLast(), false, "Unable to read headers for skycell.");
+            psFree(view);
+            return false;
+        }
+        view->chip = 0;
+        view->cell = 0;
+        view->readout = 0;
+        pmCell *source = pmFPAfileThisCell(config->files, view, "PSWARP.SKYCELL"); ///< Source cell
+        pmHDU *hdu = pmHDUFromCell(source); ///< HDU for source
+        if (!hdu || !hdu->header) {
+            psError(PM_ERR_PROG, false, "Unable to find header for sky cell.");
+            psFree(view);
+            return false;
+        }
+        int numCols = psMetadataLookupS32(NULL, hdu->header, "NAXIS1"); ///< Number of columns
+        int numRows = psMetadataLookupS32(NULL, hdu->header, "NAXIS2"); ///< Number of rows
+        if ((numCols == 0) || (numRows == 0)) {
+            psError(PSWARP_ERR_DATA, false, "skycell has invalid dimensions %d x %d", numCols, numRows);
+            psFree(view);
+            return false;
+        }
+
+        pmCell *target = pmFPAviewThisCell(view, output->fpa); ///< Target cell
+        pmReadout *readout = pmReadoutAlloc(target); ///< Target readout
+        readout->image = psImageAlloc(numCols / output->xBin, numRows / output->yBin, PS_TYPE_F32);
+        psImageInit(readout->image, NAN);
+        psFree(readout);                // Drop reference
+
+        bool status = false;
+        psMetadataItemSupplement(&status, target->concepts, source->concepts, "CELL.XBIN");
+        psMetadataItemSupplement(&status, target->concepts, source->concepts, "CELL.YBIN");
+/* 	psMetadataAddS32(target->concepts,PS_LIST_TAIL,"CELL.XBIN",PS_META_REPLACE,"",output->xBin); */
+/* 	psMetadataAddS32(target->concepts,PS_LIST_TAIL,"CELL.YBIN",PS_META_REPLACE,"",output->yBin); */
+        psMetadataItemSupplement(&status, target->concepts, source->concepts, "CELL.XSIZE");
+        psMetadataItemSupplement(&status, target->concepts, source->concepts, "CELL.YSIZE");
+/* 	psMetadataAddS32(target->concepts,PS_LIST_TAIL,"CELL.XSIZE",PS_META_REPLACE,"",numCols / output->xBin); */
+/* 	psMetadataAddS32(target->concepts,PS_LIST_TAIL,"CELL.YSIZE",PS_META_REPLACE,"",numRows / output->yBin); */
+        psMetadataItemSupplement(&status, target->concepts, source->concepts, "CELL.XPARITY");
+        psMetadataItemSupplement(&status, target->concepts, source->concepts, "CELL.YPARITY");
+        psMetadataItemSupplement(&status, target->concepts, source->concepts, "CELL.X0");
+        psMetadataItemSupplement(&status, target->concepts, source->concepts, "CELL.Y0");
+
+	
+    }
+
+    // XXX this is not a sufficient test
+    view->chip = 0;
+    view->cell = 0;
+    view->readout = -1;
+    pmHDU *phu = pmFPAviewThisPHU(view, skycell->fpa); ///< Skycell PHU
+    pmHDU *hdu = pmFPAviewThisHDU(view, skycell->fpa); ///< Skycell header
+
+    pmAstromWCS *WCS = pmAstromWCSfromHeader(hdu->header);
+
+    double cd1f = 1.0 * output->xBin;
+    double cd2f = 1.0 * output->yBin;
+    
+    WCS->crpix1 = WCS->crpix1 / cd1f;
+    WCS->crpix2 = WCS->crpix2 / cd2f;
+    
+    WCS->cdelt1 *= cd1f;
+    WCS->cdelt2 *= cd2f;
+
+    WCS->trans->x->coeff[1][0] *= cd1f;
+    WCS->trans->x->coeff[0][1] *= cd2f;
+    WCS->trans->y->coeff[1][0] *= cd1f;
+    WCS->trans->y->coeff[0][1] *= cd2f;
+    
+    
+    pmAstromWCStoHeader (hdu->header,WCS);
+
+    bool bilevelAstrometry = false;
+    if (phu) {
+        char *ctype = psMetadataLookupStr(NULL, phu->header, "CTYPE1");
+        if (ctype) {
+            bilevelAstrometry = !strcmp(&ctype[4], "-DIS");
+        }
+    }
+
+    // We read from the skycell into the output.  i.e., the output receives the desired astrometry.
+    pmChip *outputChip = pmFPAviewThisChip(view, output->fpa); ///< Chip in the output
+    if (bilevelAstrometry) {
+        if (!pmAstromReadBilevelMosaic(output->fpa, phu->header)) {
+            psError(psErrorCodeLast(), false, "Unable to read bilevel mosaic astrometry for skycell.");
+            psFree(view);
+            return false;
+        }
+        if (!pmAstromReadBilevelChip(outputChip, hdu->header)) {
+            psError(psErrorCodeLast(), false, "Unable to read bilevel chip astrometry for skycell.");
+            psFree(view);
+            return false;
+        }
+    } else {
+        // we use a default FPA pixel scale of 1.0
+      if (!pmAstromReadWCS(output->fpa, outputChip, hdu->header, 1.0)) {
+            psError(psErrorCodeLast(), false, "Unable to read WCS astrometry for skycell.");
+            psFree(view);
+            return false;
+        }
+    }
+
+    
+    view->chip = view->cell = view->readout = -1;
+    pmFPAAddSourceFromView(output->fpa, view, output->format);
+
+
+    psFree (view);
+    return true;
+}