Check BDS50 on out of range values

Author: Douglasdc3

src/main/java/aero/t2s/modes/decoder/df/bds/Bds50.java

@@ -204,22 +204,13 @@ public Bds50(short[] data) {
             return;
         }
 
-        // If known check if roll angle & track angle rate matches expected / value
-        // Formula from SkyBrary TurnRate (1) = (TAS / 10) => Roll Angle
-        // Which we can rewrite to Roll Angle * 10 * Turn Rate = TAS
-        // When TAS is not known we can use GS instead allow for bigger margin
-        if (statusTrackAngle && statusRollAngle && trackAngleRate != 0) {
-            double expectedTAS = Math.abs(rollAngle * 10d * (trackAngleRate / 3d));
-            if (statusTas) {
-                if (Math.abs(expectedTAS - tas) > 50) {
-                    invalidate();
-                    return;
-                }
-            } else if (statusGs) {
-                if (Math.abs(expectedTAS - gs) > 150) {
-                    invalidate();
-                    return;
-                }
+        // Check if values are way off th scale.
+        // We can only check large values
+        if ((statusTas || statusGs) && statusTrackAngle && statusRollAngle && Math.abs(trackAngleRate) > 0.25 && Math.abs(rollAngle) > 5) {
+            // We cannot have a rate one turn at 180 knots or greater at less than 30 degrees of bank
+            if ((gs > 180 || tas > 180) && rollAngle < 30 && trackAngleRate > 3) {
+                invalidate();
+                return;
             }
         }
     }

src/test/java/aero/t2s/modes/decoder/df/DfRealMessageTest.java

@@ -289,6 +289,56 @@ public void test_df21_bds50_485209() throws UnknownDownlinkFormatException {
         assertEquals(31.8, bds.getTrueTrack(), 0.1);
     }
 
+    @Test
+    public void test_df21_bds50_484FDF() throws UnknownDownlinkFormatException {
+        DownlinkFormat df = testMessage("A800080080502D2A600CA9DF5877");
+
+        assertInstanceOf(DF21.class, df);
+        DF21 df21 = (DF21) df;
+        assertEquals("484FDF", df.getIcao()); // Military / corrupt transponder
+        assertEquals(1000, df21.getModeA());
+
+        assertTrue(df21.isValid());
+        assertInstanceOf(Bds50.class, df21.getBds());
+
+        Bds50 bds = (Bds50) df21.getBds();
+        assertTrue(bds.isStatusGs());
+        assertEquals(338, bds.getGs(), 0.1);
+        assertTrue(bds.isStatusTas());
+        assertEquals(338, bds.getTas(), 0.1);
+        assertTrue(bds.isStatusRollAngle());
+        assertEquals(0.35, bds.getRollAngle(), 0.1);
+        assertTrue(bds.isStatusTrueAngleRate());
+        assertEquals(0, bds.getTrackAngleRate(), 0.1);
+        assertTrue(bds.isStatusTrackAngle());
+        assertEquals(3.8, bds.getTrueTrack(), 0.1);
+    }
+
+    @Test
+    public void test_df20_bds50_48418A() throws UnknownDownlinkFormatException {
+        DownlinkFormat df = testMessage("A0000E978F1FBD316114BDA0FFBF");
+
+        assertInstanceOf(DF20.class, df);
+        DF20 df20 = (DF20) df;
+        assertEquals("48418A", df.getIcao()); // Military / corrupt transponder
+        assertEquals(22375, df20.getAltitude().getAltitude());
+
+        assertTrue(df20.isValid());
+        assertInstanceOf(Bds50.class, df20.getBds());
+
+        Bds50 bds = (Bds50) df20.getBds();
+        assertTrue(bds.isStatusGs());
+        assertEquals(394, bds.getGs(), 0.1);
+        assertTrue(bds.isStatusTas());
+        assertEquals(378, bds.getTas(), 0.1);
+        assertTrue(bds.isStatusRollAngle());
+        assertEquals(21, bds.getRollAngle(), 0.1);
+        assertTrue(bds.isStatusTrueAngleRate());
+        assertEquals(1, bds.getTrackAngleRate(), 0.1);
+        assertTrue(bds.isStatusTrackAngle());
+        assertEquals(354, bds.getTrueTrack(), 0.1);
+    }
+
 
     private DownlinkFormat testMessage(String message) throws UnknownDownlinkFormatException {
         Decoder decoder = new Decoder(new HashMap<>(), 50, 2, ModeSDatabase.createDatabase());