Improve BDS50/60 detection based on inverse rocd on irs/baro

Author: Douglasdc3

src/main/java/aero/t2s/modes/decoder/df/bds/Bds60.java

@@ -106,6 +106,14 @@ public Bds60(short[] data) {
             }
         }
 
+        if ((irsRocd > 0 && baroRocd < 0) || (irsRocd < 0 && baroRocd > 0)) {
+            // Aircraft cannot be climbing and descending at the same time
+            if (Math.abs(irsRocd) > 1000 && Math.abs(baroRocd) > 1000) {
+                invalidate();
+                return;
+            }
+        }
+
         if (statusMach && statusIas && data[0] >>> 3 == 20) {
             double altitude = AltitudeEncoding.decode((data[2] & 0x1F) << 8 | data[3]).getAltitude();
             if (altitude > 0) {

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

@@ -340,7 +340,7 @@ public void test_df20_bds50_48418A() throws UnknownDownlinkFormatException {
     }
 
     @Test
-    public void test_df16_bds50_48418A() throws UnknownDownlinkFormatException {
+    public void test_df16_02A198() throws UnknownDownlinkFormatException {
         DownlinkFormat df = testMessage("80C18819584195384EF8505941FD");
 
         assertInstanceOf(DF16.class, df);
@@ -366,6 +366,32 @@ public void test_df16_bds50_48418A() throws UnknownDownlinkFormatException {
         assertFalse(df16.isRANotTurnRight());
     }
 
+    @Test
+    public void test_df21_bds50_02A185() throws UnknownDownlinkFormatException {
+        DownlinkFormat df = testMessage("A8001AA0F4596112BDFC569A3AEC");
+
+        assertInstanceOf(DF21.class, df);
+        DF21 df21 = (DF21) df;
+        assertEquals("02A185", df.getIcao()); // Military / corrupt transponder
+        assertEquals(7110, df21.getModeA());
+
+        assertFalse(df21.isMultipleMatches());
+        assertTrue(df21.isValid());
+        assertEquals(Bds50.class, df21.getBds().getClass());
+
+        Bds50 bds = (Bds50) df21.getBds();
+        assertTrue(bds.isStatusGs());
+        assertEquals(148, bds.getGs(), 0.1);
+        assertTrue(bds.isStatusTas());
+        assertEquals(172, bds.getTas(), 0.1);
+        assertTrue(bds.isStatusRollAngle());
+        assertEquals(-16.5, bds.getRollAngle(), 0.1);
+        assertTrue(bds.isStatusTrueAngleRate());
+        assertEquals(-2.0, bds.getTrackAngleRate(), 0.1);
+        assertTrue(bds.isStatusTrackAngle());
+        assertEquals(210.9, bds.getTrueTrack(), 0.1);
+    }
+
     private DownlinkFormat testMessage(String message) throws UnknownDownlinkFormatException {
         Decoder decoder = new Decoder(new HashMap<>(), 50, 2, ModeSDatabase.createDatabase());