Add --max-range parameter. Use it for relative position limits, and to discard bad position results.

(cherry picked from commit 0d725508f78cb2fd7759efbb66b45b867d6f7722)

debian/config-template

@@ -52,6 +52,11 @@ AGGRESSIVE=
 LAT=
 LON=
 
+# If set, provides the absolute maximum receiver range used to
+# filter bad position reports, and to determine when local position
+# decoding is safe to use. Specify this in nautical miles (NM).
+MAX_RANGE=
+
 #
 # Networking options
 #

debian/dump1090-mutability.config

@@ -30,6 +30,7 @@ if [ -e $CONFIGFILE ]; then
   db_set_yn $NAME/decode-aggressive "$AGGRESSIVE"
   db_set $NAME/decode-lat "$LAT"
   db_set $NAME/decode-lon "$LON"
+  db_set $NAME/decode-max-range "$MAX_RANGE"
 
   db_set $NAME/net-http-port "$HTTP_PORT"
   db_set $NAME/net-ri-port "$RAW_INPUT_PORT"
@@ -178,6 +179,7 @@ db_go || true; db_get $NAME/auto-start; if [ "$RET" = "true" ]; then
 
  db_input low $NAME/decode-fix-crc || true
  db_input low $NAME/decode-aggressive || true
+ db_input_verify medium $NAME/decode-max-range is_number || true
  db_input_verify medium $NAME/decode-lat is_number_or_empty || true
 
  db_go || true; db_get $NAME/decode-lat; if [ -n "$RET" ]; then

debian/dump1090-mutability.init

@@ -42,6 +42,7 @@ SCRIPTNAME=/etc/init.d/$NAME
 [ -z "$FATSV_OUTPUT_PORT" ] && FATSV_OUTPUT_PORT=0
 [ -z "$NET_BUFFER" ] && NET_BUFFER=0
 [ -z "$JSON_INTERVAL" ] && JSON_INTERVAL=0
+[ -z "$MAX_RANGE" ] && MAX_RANGE=300
 
 # receiver:
 case "x$DEVICE" in
@@ -63,6 +64,7 @@ if [ "x$PHASE_ENHANCE" = "xyes" ]; then ARGS="$ARGS --phase-enhance"; fi
 if [ "x$AGGRESSIVE" = "xyes" ]; then ARGS="$ARGS --aggressive"; fi
 if [ -n "$LAT" ]; then ARGS="$ARGS --lat $LAT"; fi
 if [ -n "$LON" ]; then ARGS="$ARGS --lon $LON"; fi
+ARGS="$ARGS --max-range $MAX_RANGE"; fi
 
 # net:
 

debian/dump1090-mutability.postinst

@@ -69,6 +69,7 @@ case "$1" in
         subvar_yn decode-aggressive AGGRESSIVE
         subvar decode-lat LAT
         subvar decode-lon LON
+        subvar decode-max-range MAX_RANGE
         subvar net-http-port HTTP_PORT
         subvar net-ri-port RAW_INPUT_PORT
         subvar net-ro-port RAW_OUTPUT_PORT

debian/dump1090-mutability.templates

@@ -102,6 +102,23 @@ Description: Longitude of receiver, in decimal degrees:
 Type: string
 Default:
 
+Template: dump1090-mutability/decode-max-range
+Description: Absolute maximum range of receiver, in nautical miles:
+ If the maximum range of the receiver is provided, dump1090 can filter
+ out impossible position reports that are due to aircraft that transmit
+ bad data.
+ .
+ Additionally, if the maximum range is larger than 180NM, when local
+ position decoding is used (when insufficient position messages
+ have been received for global position decoding), it is limited to
+ only those positions that would unambiguously decode to a single
+ position within the given receiver range.
+ .
+ This range should be the absolute maximum range - any position data
+ from further away will be entirely discarded!
+Type: string
+Default: 300
+
 Template: dump1090-mutability/net-http-port
 Description: Port for internal webserver (0 disables):
  dump1090 can provide an internal webserver that serves a basic "virtual