Tested other reference (FPN mitigation) with initial orientation

src/main/java/com/elphel/imagej/tileprocessor/QuadCLTCPU.java

@@ -654,8 +654,8 @@ public class QuadCLTCPU {
     			{0.25*wh[0],0.75*wh[1]},
     			{0.75*wh[0],0.75*wh[1]}};
     	}
-    	double s2 = 0.0;
-    	for (double [] xy:xy_pairs) {
+    	double s2 = 0.0, s0=0.0;
+    	for (double [] xy:xy_pairs) if (xy != null){
     		double [] pXpYD = ers.getImageCoordinatesERS(
     				null, // QuadCLT cameraQuadCLT, // camera station that got image to be to be matched 
     				xy[0], // double px,                // pixel coordinate X in the reference view
@@ -668,11 +668,16 @@ public class QuadCLTCPU {
     				xyzatr1[0], // double [] camera_xyz,     // camera center in world coordinates
     				xyzatr1[1], // double [] camera_atr,     // camera orientation relative to world frame
     				OpticalFlow.LINE_ERR); // double    line_err);       // threshold error in scan lines (1.0)
-    		double dx = pXpYD[0]-xy[0];
-    		double dy = pXpYD[1]-xy[1];
-    		s2 += dx*dx+dy*dy;
+    		if (pXpYD != null) {
+    			double dx = pXpYD[0]-xy[0]; // null pointer
+    			double dy = pXpYD[1]-xy[1];
+    			s2 += dx*dx+dy*dy;
+    			s0+=1.0;
+    		} else {
+    			continue;
+    		}
     	}
-    	double offs_avg = Math.sqrt(s2/xy_pairs.length);
+    	double offs_avg = Math.sqrt(s2/s0);
     	return offs_avg;
     }