Track CPR encoding type directly rather than inferring it from airground.

(airground can change even while airborne if SPI/Alert status gets set)

dump1090.h

@@ -198,6 +198,10 @@ typedef enum {
     SIL_PER_SAMPLE, SIL_PER_HOUR
 } sil_type_t;
 
+typedef enum {
+    CPR_SURFACE, CPR_AIRBORNE, CPR_COARSE
+} cpr_type_t;
+
 #define MODES_NON_ICAO_ADDRESS       (1<<24) // Set on addresses to indicate they are not ICAO addresses
 
 #define MODES_DEBUG_DEMOD (1<<0)
@@ -461,6 +465,7 @@ struct modesMessage {
     // valid if category_valid
     unsigned category;          // A0 - D7 encoded as a single hex byte
     // valid if cpr_valid
+    cpr_type_t cpr_type;        // The encoding type used (surface, airborne, coarse TIS-B)
     unsigned cpr_lat;           // Non decoded latitude.
     unsigned cpr_lon;           // Non decoded longitude.
     unsigned cpr_nucp;          // NUCp/NIC value implied by message type

mode_s.c

@@ -903,6 +903,7 @@ static void decodeESSurfacePosition(struct modesMessage *mm, int check_imf)
     mm->cpr_odd = getbit(me, 22);
     mm->cpr_nucp = (14 - mm->metype);
     mm->cpr_valid = 1;
+    mm->cpr_type = CPR_SURFACE;
 
     unsigned movement = getbits(me, 6, 12);
     if (movement > 0 && movement < 125) {
@@ -948,6 +949,7 @@ static void decodeESAirbornePosition(struct modesMessage *mm, int check_imf)
         } else {
             // Otherwise, assume it's valid.
             mm->cpr_valid = 1;
+            mm->cpr_type = CPR_AIRBORNE;
             mm->cpr_odd = getbit(me, 22);
 
             if (mm->metype == 18 || mm->metype == 22)
@@ -1386,6 +1388,19 @@ static const char *addrtype_to_string(addrtype_t type) {
     }
 }
 
+static const char *cpr_type_to_string(cpr_type_t type) {
+    switch (type) {
+    case CPR_SURFACE:
+        return "Surface";
+    case CPR_AIRBORNE:
+        return "Airborne";
+    case CPR_COARSE:
+        return "TIS-B Coarse";
+    default:
+        return "unknown CPR type";
+    }
+}
+
 static void print_hex_bytes(unsigned char *data, size_t len) {
     size_t i;
     for (i = 0; i < len; ++i) {
@@ -1676,12 +1691,11 @@ void displayModesMessage(struct modesMessage *mm) {
                mm->category);
     }
 
-    if (mm->msgtype == 17 || mm->msgtype == 18) {
-    }
-
     if (mm->cpr_valid) {
-        printf("  CPR odd flag:  %s\n"
+        printf("  CPR type:      %s\n"
+               "  CPR odd flag:  %s\n"
                "  CPR NUCp/NIC:  %u\n",
+               cpr_type_to_string(mm->cpr_type),
                mm->cpr_odd ? "odd" : "even",
                mm->cpr_nucp);
 

track.c

@@ -260,7 +260,7 @@ static int doGlobalCPR(struct aircraft *a, struct modesMessage *mm, uint64_t now
 {
     int result;
     int fflag = mm->cpr_odd;
-    int surface = (mm->airground == AG_GROUND);
+    int surface = (mm->cpr_type == CPR_SURFACE);
 
     *nuc = (a->cpr_even_nuc < a->cpr_odd_nuc ? a->cpr_even_nuc : a->cpr_odd_nuc); // worst of the two positions
 
@@ -341,7 +341,7 @@ static int doLocalCPR(struct aircraft *a, struct modesMessage *mm, uint64_t now,
     double range_limit = 0;
     int result;
     int fflag = mm->cpr_odd;
-    int surface = (mm->airground == AG_GROUND);
+    int surface = (mm->cpr_type == CPR_SURFACE);
 
     *nuc = mm->cpr_nucp;
 
@@ -426,7 +426,7 @@ static void updatePosition(struct aircraft *a, struct modesMessage *mm, uint64_t
     unsigned new_nuc = 0;
     int surface;
 
-    surface = (mm->airground == AG_GROUND);
+    surface = (mm->cpr_type == CPR_SURFACE);
 
     if (surface) {
         ++Modes.stats_current.cpr_surface;
@@ -446,7 +446,7 @@ static void updatePosition(struct aircraft *a, struct modesMessage *mm, uint64_t
     // If we have enough recent data, try global CPR
     if (trackDataValid(&a->cpr_odd_valid) && trackDataValid(&a->cpr_even_valid) &&
         a->cpr_odd_valid.source == a->cpr_even_valid.source &&
-        a->cpr_odd_airground == a->cpr_even_airground &&
+        a->cpr_odd_type == a->cpr_even_type &&
         time_between(a->cpr_odd_valid.updated, a->cpr_even_valid.updated) <= max_elapsed) {
 
         location_result = doGlobalCPR(a, mm, now, &new_lat, &new_lon, &new_nuc);
@@ -607,7 +607,7 @@ struct aircraft *trackUpdateFromMessage(struct modesMessage *mm)
 
     // CPR, even
     if (mm->cpr_valid && !mm->cpr_odd && accept_data(&a->cpr_even_valid, mm->source, now)) {
-        a->cpr_even_airground = mm->airground;
+        a->cpr_even_type = mm->cpr_type;
         a->cpr_even_lat = mm->cpr_lat;
         a->cpr_even_lon = mm->cpr_lon;
         a->cpr_even_nuc = mm->cpr_nucp;
@@ -615,7 +615,7 @@ struct aircraft *trackUpdateFromMessage(struct modesMessage *mm)
 
     // CPR, odd
     if (mm->cpr_valid && mm->cpr_odd && accept_data(&a->cpr_odd_valid, mm->source, now)) {
-        a->cpr_odd_airground = mm->airground;
+        a->cpr_odd_type = mm->cpr_type;
         a->cpr_odd_lat = mm->cpr_lat;
         a->cpr_odd_lon = mm->cpr_lon;
         a->cpr_odd_nuc = mm->cpr_nucp;

track.h

@@ -119,13 +119,13 @@ struct aircraft {
     airground_t   airground;      // air/ground status
 
     data_validity cpr_odd_valid;        // Last seen even CPR message
-    airground_t   cpr_odd_airground;
+    cpr_type_t    cpr_odd_type;
     unsigned      cpr_odd_lat;
     unsigned      cpr_odd_lon;
     unsigned      cpr_odd_nuc;
 
     data_validity cpr_even_valid;       // Last seen odd CPR message
-    airground_t   cpr_even_airground;
+    cpr_type_t    cpr_even_type;
     unsigned      cpr_even_lat;
     unsigned      cpr_even_lon;
     unsigned      cpr_even_nuc;