allow rough receiver location to wander gradually

only if receiver extent becomes quite large

net_io.c

@@ -5486,7 +5486,7 @@ void modesNetPeriodicWork(void) {
 
  if (Modes.receiverTable) {
  static uint32_t upcount;
- int nParts = 5 * MINUTES / free_client_interval;
+ int nParts = RECEIVER_MAINTENANCE_INTERVAL / free_client_interval;
  receiverTimeout((upcount % nParts), nParts, now);
  upcount++;
  }

receiver.c

@@ -47,8 +47,35 @@ struct receiver *receiverCreate(uint64_t id) {
  fprintf(stderr, "receiverCount: %"PRIu64"\n", Modes.receiverCount);
  return r;
 }
-//static void receiverMaintenance(struct receiver *re) {
-//}
+static void receiverDebugPrint(struct receiver *r, char *message) {
+ if (1) {
+ return;
+ }
+ fprintf(stderr, "%016"PRIx64" %9lld %6.1f %6.1f %6.1f %6.1f %s\n",
+ r->id, (long long) r->positionCounter,
+ r->latMin, r->latMax, r->lonMin, r->lonMax,
+ message);
+}
+static void receiverMaintenance(struct receiver *r) {
+ double decay = 0.005 * RECEIVER_MAINTENANCE_INTERVAL / SECONDS;
+
+ receiverDebugPrint(r, "beforeDecay");
+
+ // only decay if extent is pretty large
+
+ if (r->latMax - r->latMin > 10) {
+ r->latMax -= decay;
+ r->latMin += decay;
+ }
+
+ if (r->lonMax - r->lonMin > 10) {
+ r->lonMax -= decay;
+ r->lonMin += decay;
+ }
+
+ receiverDebugPrint(r, "afterDecay");
+
+}
 void receiverTimeout(int part, int nParts, int64_t now) {
  if (!Modes.receiverTable) {
  return;
@@ -78,7 +105,7 @@ void receiverTimeout(int part, int nParts, int64_t now) {
  Modes.receiverCount--;
  free(del);
  } else {
- //receiverMaintenance(*r);
+ receiverMaintenance(*r);
  r = &(*r)->next;
  }
  }
@@ -158,6 +185,14 @@ int receiverPositionReceived(struct aircraft *a, struct modesMessage *mm, double
 
  r->lonMax = fmax(r->lonMax, lon);
  r->latMax = fmax(r->latMax, lat);
+ if (
+ before.latMin != r->latMin
+ || before.latMax != r->latMax
+ || before.lonMin != r->lonMin
+ || before.lonMax != r->lonMax
+ ) {
+ //receiverDebugPrint(r, "growingExtent");
+ }
  r->goodCounter++;
  r->badCounter = fmax(0, r->badCounter - 0.5);
  }

receiver.h

@@ -7,6 +7,8 @@
 #define RECEIVER_RANGE_BAD (-7)
 #define RECEIVER_RANGE_UNCLEAR (-1)
 
+#define RECEIVER_MAINTENANCE_INTERVAL (5 * MINUTES)
+
 struct bad_ac {
  uint32_t addr;
  int64_t ts;