Add BDS21 Registration & Airline

Author: Douglasdc3

README.md

@@ -112,7 +112,7 @@ We hope with more BDS implemented the guessing accuracy will improve.
 | 1,E | Mode S services GICB capability report     | ❌        |
 | 1,F | Mode S services GICB capability report     | ❌        |
 | 2,0 | Aircraft Identification                    | ✅        |
-| 2,1 | Aircraft and Airline registration marking  | ❌        |
+| 2,1 | Aircraft and Airline registration marking  | ⚠️        | Experimental
 | 2,2 | Antenna positions                          | ❌        |
 | 2,5 | Antenna type                               | ❌        |
 | 3,0 | ACAS Active resolution advisory            | ❌        | Detection implemented, decoding missing

mode-s/src/main/java/aero/t2s/modes/decoder/df/bds/Bds21.java

@@ -0,0 +1,55 @@
+package aero.t2s.modes.decoder.df.bds;
+
+import aero.t2s.modes.Track;
+import aero.t2s.modes.decoder.Common;
+
+public class Bds21 extends Bds {
+    @Override
+    public boolean attemptDecode(Track track, short[] data) {
+        if (track.getCapabilityReport().isAvailable() && !track.getCapabilityReport().isBds21()) {
+            return false;
+        }
+
+        boolean aircraftRegistrationStatus = (data[4] & 0b10000000) != 0;
+        boolean airlineRegistrationStatus = (data[9] & 0b00010000) != 0;
+
+        if (!aircraftRegistrationStatus && (data[4] | data[5] | data[6] | data[7] | data[8] | data[9] >>> 5) != 0) {
+            return false;
+        }
+
+        if (!airlineRegistrationStatus && ((data[9] & 0b00001111) | data[10]) != 0) {
+            return false;
+        }
+
+        if (aircraftRegistrationStatus) {
+            String registration = Common.charToString((data[4] & 0b01111110) >>> 1) // Char 1
+                + Common.charToString(((data[4] & 0b00000001) << 5) | (data[5] >>> 3)) // Char 2
+                + Common.charToString(((data[5] & 0b00000111) << 3) | (data[6] >>> 5)) // Char 3
+                + Common.charToString(((data[6] & 0b00011111) << 1) | (data[7] >>> 7)) // Char 4
+                + Common.charToString((data[7] & 0b01111110) >>> 1) // Char 5
+                + Common.charToString(((data[7] & 0b00000001) << 5) | (data[8] >>> 3)) // Char 6
+                + Common.charToString(((data[8] & 0b00000111) << 3) | (data[9] >>> 3)) // Char 7
+                ;
+
+
+            if (registration.contains("#")) {
+                return false;
+            }
+
+            track.setRegistration(registration.replace("_", ""));
+        }
+
+        if (airlineRegistrationStatus) {
+            String airline = Common.charToString(((data[9] & 0b00001111) << 2 | (data[10] >>> 6)))
+                + Common.charToString(data[10] & 0b00111111);
+
+            if (airline.contains("_") || airline.contains("#")) {
+                return false;
+            }
+
+            track.setOperator(airline);
+        }
+
+        return true;
+    }
+}

mode-s/src/main/java/aero/t2s/modes/decoder/df/bds/BdsDecoder.java

@@ -20,6 +20,7 @@ public BdsDecoder() {
         bdsDecoder.add(new Bds50());
         bdsDecoder.add(new Bds53());
         bdsDecoder.add(new Bds60());
+        bdsDecoder.add(new Bds21());
     }
 
     public boolean decode(Track track, short[] data) {
@@ -30,8 +31,6 @@ public boolean decode(Track track, short[] data) {
 
         for (Bds bds : bdsDecoder) {
             if (bds.attemptDecode(track, data)) {
-                LoggerFactory.getLogger(getClass()).debug("Matched {}", bds.getClass().getSimpleName());
-
                 return true;
             }
         }