Merge pull request #19 from wiedehopf/cpr_fix

Some improvements for position updating / CPR handling

track.c

@@ -516,11 +516,19 @@ static void updatePosition(struct aircraft *a, struct modesMessage *mm) {
  fprintf(stderr, "global CPR failure (invalid) for (%06X).\n", a->addr);
 #endif
  // Global CPR failed because the position produced implausible results.
- // This is bad data. Discard both odd and even messages and wait for a fresh pair.
- // Also disable aircraft-relative positions until we have a new good position (but don't discard the
- // recorded position itself)
+ // This is bad data. In case the previously decoded (current)
+ // position is incorrect, reduce the 70 second expires timer by 25
+ // seconds, so repeated failures will lead to invalidation of the
+ // current position and a new position can be determined. Without
+ // this a bad current position might block valid new positions for
+ // up to a minute due to the speed check.
+
  Modes.stats_current.cpr_global_bad++;
- a->cpr_odd_valid.source = a->cpr_even_valid.source = a->position_valid.source = SOURCE_INVALID;
+
+ a->cpr_odd_valid.expires -= 25;
+ a->cpr_even_valid.expires -= 25;
+ a->position_valid.expires -= 25;
+
 
  return;
  } else if (location_result == -1) {
@@ -806,6 +814,7 @@ static int altitude_to_feet(int raw, altitude_unit_t unit) {
 
 struct aircraft *trackUpdateFromMessage(struct modesMessage *mm) {
  struct aircraft *a;
+ unsigned int cpr_new = 0;
 
  if (mm->msgtype == 32) {
  // Mode A/C, just count it (we ignore SPI)
@@ -1014,6 +1023,7 @@ struct aircraft *trackUpdateFromMessage(struct modesMessage *mm) {
  a->cpr_even_lat = mm->cpr_lat;
  a->cpr_even_lon = mm->cpr_lon;
  compute_nic_rc_from_message(mm, a, &a->cpr_even_nic, &a->cpr_even_rc);
+ cpr_new = 1;
  }
 
  // CPR, odd
@@ -1022,6 +1032,7 @@ struct aircraft *trackUpdateFromMessage(struct modesMessage *mm) {
  a->cpr_odd_lat = mm->cpr_lat;
  a->cpr_odd_lon = mm->cpr_lon;
  compute_nic_rc_from_message(mm, a, &a->cpr_odd_nic, &a->cpr_odd_rc);
+ cpr_new = 1;
  }
 
  if (mm->accuracy.sda_valid && accept_data(&a->sda_valid, mm->source)) {
@@ -1073,8 +1084,8 @@ struct aircraft *trackUpdateFromMessage(struct modesMessage *mm) {
  combine_validity(&a->altitude_geom_valid, &a->altitude_baro_valid, &a->geom_delta_valid);
  }
 
- // If we've got a new cprlat or cprlon
- if (mm->cpr_valid) {
+ // If we've got a new cpr_odd or cpr_even
+ if (cpr_new) {
  updatePosition(a, mm);
  }