Index: /branches/czw_branch/cleanup/Ohana/src/getstar/src/MatchCoords.c
===================================================================
--- /branches/czw_branch/cleanup/Ohana/src/getstar/src/MatchCoords.c	(revision 25151)
+++ /branches/czw_branch/cleanup/Ohana/src/getstar/src/MatchCoords.c	(revision 25152)
@@ -40,5 +40,4 @@
     // Xi[4] = Xi[0]; Yi[4] = Yi[0];
 
-
     ymin = xmin = +FLT_MAX;
     ymax = xmax = -FLT_MAX;
@@ -52,5 +51,10 @@
     // transform input point to image coords
     double x, y;
-    RD_to_XY(&x, &y, ra, dec, &dbImages[i].coords);
+    int status = RD_to_XY(&x, &y, ra, dec, &dbImages[i].coords);
+
+    if (!status) {
+        // avoid matching antipodal skycells
+        continue;
+    }
 
     if ((x >= xmin && x <= xmax) && (y >= ymin && y <= ymax)) {
Index: /branches/czw_branch/cleanup/ppStack/src/ppStackCombineFinal.c
===================================================================
--- /branches/czw_branch/cleanup/ppStack/src/ppStackCombineFinal.c	(revision 25151)
+++ /branches/czw_branch/cleanup/ppStack/src/ppStackCombineFinal.c	(revision 25152)
@@ -60,10 +60,12 @@
         sumWeights += weight;
     }
-    pmReadout *outRO = options->outRO;  // Output readout
-    outRO->covariance = psImageCovarianceSum(options->covariances);
-    psBinaryOp(outRO->covariance->image, outRO->covariance->image, "/",
-               psScalarAlloc(sumWeights, PS_TYPE_F32));
-    psFree(options->covariances); options->covariances = NULL;
-    psImageCovarianceTransfer(outRO->variance, outRO->covariance);
+    if (sumWeights > 0.0) {
+        pmReadout *outRO = options->outRO;  // Output readout
+        outRO->covariance = psImageCovarianceSum(options->covariances);
+        psBinaryOp(outRO->covariance->image, outRO->covariance->image, "/",
+                   psScalarAlloc(sumWeights, PS_TYPE_F32));
+        psFree(options->covariances); options->covariances = NULL;
+        psImageCovarianceTransfer(outRO->variance, outRO->covariance);
+    }
 
 #ifdef TESTING