Add sanity checks and additional tests that exercise both Global and Local position updates, both Airborne and Surface.

Author: IDBeswick

README.md

@@ -34,10 +34,10 @@ Most features of the DF17/18 protocol have been implemented, some message lack s
 | 2         | Aircraft Identification      | ✅         |                                                           |
 | 3         | Aircraft Identification      | ✅         |                                                           |
 | 4         | Aircraft Identification      | ✅         |                                                           |
-| 5         | Surface Position             | ❌         | Not implemented yet                                       |
-| 6         | Surface Position             | ❌         | Not implemented yet                                       |
-| 7         | Surface Position             | ❌         | Not implemented yet                                       |
-| 8         | Surface Position             | ❌         | Not implemented yet                                       |
+| 5         | Surface Position             | ✅         |                                                           |
+| 6         | Surface Position             | ✅         |                                                           |
+| 7         | Surface Position             | ✅         |                                                           |
+| 8         | Surface Position             | ✅         |                                                           |
 | 9         | Airborne Position            | ✅         |                                                           |
 | 10        | Airborne Position            | ✅         |                                                           |
 | 11        | Airborne Position            | ✅         |                                                           |

src/main/java/aero/t2s/modes/decoder/df/df17/PositionUpdate.java

@@ -1,17 +1,21 @@
 package aero.t2s.modes.decoder.df.df17;
 
 import aero.t2s.modes.CprPosition;
+import org.slf4j.LoggerFactory;
+
 import java.util.*;
 
 public class PositionUpdate {
-    private static double originLat;                // Origin is passed-in as a command-line argument as an indication of where the receiver is located
+    private static double originLat;                        // Origin is passed-in as a command-line argument as an indication of where the receiver is located
     private static double originLon;
 
-    private static double receiverLat;              // Receiver position is calculated based on data received
+    private static final double updateThreshold = 0.5d;     // Positions which move between updates by more than this (in degrees) should be rejected
+    private static final double receiverRange = 4.0d;       // Positions further away from the receiver than this (in degrees) should be rejected
+    private static double receiverLat;                      // Receiver position is calculated based on data received
     private static double receiverLon;
-    private static double receiverSumLat;           // Running-total of valid positions that can be used to calculate the average receiver position
+    private static double receiverSumLat;                   // Running-total of valid positions that can be used to calculate the average receiver position
     private static double receiverSumLon;
-    private static double receiverSumCount = 0;     // number of valid positions received that are used to calculate the average
+    private static double receiverSumCount = 0;             // number of valid positions received that are used to calculate the average
 
     private static Map<String, PositionUpdate> cache = new HashMap<>();
     private static Timer cacheCleanup;
@@ -70,7 +74,14 @@ private CprPosition calculate(boolean isCprEven, CprPosition newCpr) {
         }
 
         if (current != null && current.isValid()) {
-            previous = current;
+            // Sanity Check: Is the position just received too far away from the receiver position?
+            if ((Math.abs(current.getLat() - receiverLat) > receiverRange) || (Math.abs(current.getLon() - receiverLon) > receiverRange)) {
+                LoggerFactory.getLogger(getClass()).info("Position Update discarded due to outside receiver range.");
+                current = null;
+            }
+            else {
+                previous = current;
+            }
         }
 
         return current;
@@ -95,29 +106,20 @@ private void calculateLocal(boolean isOdd) {
         double newLon = dLon * (m + cpr.getLon());
 
         cpr.setZones(j, m);
-        if ((j != otherCpr.getLatZone()) || (m != otherCpr.getLonZone())) {
-            // The new frame is in a different CPR zone
-            if (isOdd) {
-                //even = null;        // Keep the current odd frame but discard the previous even frame
-            } else {
-                //odd = null;
-            }
-            //previous = null;
-            //current = null;
-            //return;
-        }
 
         current = new CprPosition(newLat, newLon, cpr.getSurface());
         if (current.getSurface()) {
             validateSurface(current);
         }
 
-        // TODO Should be a sanity-check here to make sure the calculated position isn't outside receiver origin range
-        // TODO Should be a sanity-check here to see if the calculated movement since the last update is too far
+        if ((Math.abs(current.getLat() - previous.getLat()) > updateThreshold) || (Math.abs(current.getLon() - previous.getLon()) > updateThreshold)) {
+                LoggerFactory.getLogger(getClass()).info("Position Update discarded due to unreasonable distance between updates.");
+                current = null;
+        }
     }
 
     private void calculateGlobal() {
-        double j = Math.floor(59.0 * even.getLat() - 60.0 * odd.getLat() + 0.5);
+        double j = Math.floor(dLatOdd * even.getLat() - dLatEven * odd.getLat() + 0.5);
         double degrees = even.getSurface() ? 90.0 : 360.0;  // Doesn't matter whether we check odd or even as they must both match by now
 
         double latEven = (degrees / dLatEven) * (cprMod(j, dLatEven) + even.getLat());
@@ -161,7 +163,6 @@ private void calculateGlobal() {
         if (current.getSurface()) {
             validateSurface(current);
         }
-        //TODO Should be a sanity-check here to make sure the calculated position isn't outside receiver origin range
     }
 
     static private double cprMod(double a, double b) {

src/test/java/aero/t2s/modes/decoder/df/df17/AirbornePositionTest.java

@@ -28,7 +28,7 @@ public void test_airborne_position_aircraft() throws UnknownDownlinkFormatExcept
         // We should NOT have a valid position after only one frame
         assertFalse(positionA.isPositionAvailable());
 
-        // This is an EVEN frame with Surface Position
+        // This is an EVEN frame with Airborne Position... so we should be able to do a global calculation of position
         DownlinkFormat dfB = testMessage("8d407663588303313d84f719b2de");
 
         assertInstanceOf(DF17.class, dfB);
@@ -38,14 +38,27 @@ public void test_airborne_position_aircraft() throws UnknownDownlinkFormatExcept
         assertInstanceOf(AirbornePosition.class, exSqB);
         AirbornePosition positionB = (AirbornePosition) exSqB;
         // We should now have a valid position after receiving both even and odd frames
-
         assertTrue(positionB.isPositionAvailable());
         assertEquals(52.789, positionB.getLat(), 0.01);
         assertEquals(-2.405, positionB.getLon(), 0.01);
+
+        // This is another EVEN frame with Airborne Position... so we should be able to do a local calculation of position
+        DownlinkFormat dfC = testMessage("8d407663588303312385138ddce6");
+
+        assertInstanceOf(DF17.class, dfC);
+        DF17 df17C = (DF17) dfC;
+        assertEquals("407663", df17C.getIcao());
+        ExtendedSquitter exSqC = df17C.getExtendedSquitter();
+        assertInstanceOf(AirbornePosition.class, exSqC);
+        AirbornePosition positionC = (AirbornePosition) exSqC;
+        // We should still have a valid position after receiving another even frame
+        assertTrue(positionC.isPositionAvailable());
+        assertEquals(52.788, positionC.getLat(), 0.01);
+        assertEquals(-2.401, positionC.getLon(), 0.01);
     }
 
     private DownlinkFormat testMessage(String message) throws UnknownDownlinkFormatException {
-        Decoder decoder = new Decoder(new HashMap<>(), 50, 2, ModeSDatabase.createDatabase());
+        Decoder decoder = new Decoder(new HashMap<>(), 53, -2, ModeSDatabase.createDatabase());
 
         return decoder.decode(BinaryHelper.stringToByteArray(message));
     }

src/test/java/aero/t2s/modes/decoder/df/df17/SurfacePositionTest.java

@@ -46,12 +46,25 @@ public void test_surface_position_aircraft() throws UnknownDownlinkFormatExcepti
         assertTrue(positionB.isPositionAvailable());
         assertEquals(53.3604, positionB.getLat(), 0.001);
         assertEquals(-2.2671, positionB.getLon(), 0.001);
-
         assertTrue(positionB.isVelocityAvailable());
         assertEquals(1.75, positionB.getVelocity(), 0.1);
-
         assertTrue(positionB.isTrackAvailable());
         assertEquals(230.625, positionB.getTrack(), 0.1);
+
+        // This is another ODD frame with Surface Position... so we should be able to do a local calculation of position
+        DownlinkFormat dfC = testMessage("8c4ca6a9389d27ec46497d8ea39e");
+
+        assertInstanceOf(DF17.class, dfC);
+        DF17 df17C = (DF17) dfC;
+        assertEquals("4CA6A9", df17C.getIcao());
+        ExtendedSquitter exSqC = df17C.getExtendedSquitter();
+        assertInstanceOf(SurfacePosition.class, exSqC);
+        SurfacePosition positionC = (SurfacePosition) exSqC;
+        // We should still have a valid position after receiving another odd frame
+
+        assertTrue(positionC.isPositionAvailable());
+        assertEquals(53.360, positionC.getLat(), 0.001);
+        assertEquals(-2.267, positionC.getLon(), 0.001);
     }
 
     @Test