max distance and range histogram: require certain ADS-B quality

track.c

@@ -1219,7 +1219,14 @@ static void setPosition(struct aircraft *a, struct modesMessage *mm, int64_t now
  a->receiver_distance = mm->receiver_distance;
  a->receiver_direction = bearing(Modes.fUserLat, Modes.fUserLon, a->lat, a->lon);
 
- if (mm->source == SOURCE_ADSB || mm->source == SOURCE_ADSR) {
+ // nac_p >= 2 accuracy better than 4 nmi
+ // decoded_rc less than 5 * nmi
+ if (mm->source == SOURCE_ADSB
+ && trackDataValid(&a->nac_p_valid) && a->nac_p >= 2
+ && mm->decoded_rc != 0 && mm->decoded_rc < 5 * 1852
+ ) {
+ update_range_histogram(a, now);
+ } else if (mm->source == SOURCE_ADSR) {
  update_range_histogram(a, now);
  }