CLAUDE: renderNadirSequence(): null rim tiles with corrupt grid positions

Analysis of the -NADIR-SCENE-PXPYD[-NULLCAM] dumps (graveyard ref
1763232420_274928) showed the transformFromVirtual() refinement output is
accurate to <0.3 px in the interior, but produces garbage coordinates
(5..100 px off) in a rim band at the edge of the valid region, where the
interpolation works one-sided over NaN-filled disparity. Rendered, those
tiles put wrong content in a border strip: COLMAP fit it as fake barrel
distortion (f=1000, k1=-0.38) and image-based rotation measurements were
contaminated (apparent ~0.6x roll).

A correct scene-frame grid position is the tile center + small ERS
displacement, so tiles straying more than 4 px are nulled and render as
NaN instead of wrong content, slightly shrinking the usable FOV at the rim.
Co-authored-by: Claude <claude@elphel.com>

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

@@ -10987,6 +10987,24 @@ java.lang.NullPointerException
     				scene_atr,                // final double []   scene_atr,
     				ref_scene,                // final QuadCLT     reference_QuadClt,
     				selected_scenes[nscene]); // final QuadCLT     scene_QuadClt
+    		// Null rim tiles where transformFromVirtual()'s refinement produced garbage
+    		// coordinates (one-sided interpolation over NaN-filled disparity at the edge
+    		// of the valid region - errors of 5..100 px observed). A correct grid position
+    		// is the tile center plus a small (<~2 px) ERS displacement, so a tile whose
+    		// position strays farther than max_grid_err renders wrong content and must be
+    		// skipped rather than rendered.
+    		final double max_grid_err = 4.0; // px
+    		{
+    			int tX = ref_scene.getTilesX();
+    			int tsz = ref_scene.getTileSize();
+    			for (int t = 0; t < pXpYD_scene.length; t++) if (pXpYD_scene[t] != null) {
+    				double ctrX = ((t % tX) + 0.5) * tsz;
+    				double ctrY = ((t / tX) + 0.5) * tsz;
+    				if (Math.hypot(pXpYD_scene[t][0] - ctrX, pXpYD_scene[t][1] - ctrY) > max_grid_err) {
+    					pXpYD_scene[t] = null;
+    				}
+    			}
+    		}
     		if (undistort) {
     			undistortPxPy(pXpYD_scene, selected_scenes[nscene].getErsCorrection());
     		}