From 937e7ac564b01ef151b6c961a088d87c489fba3a Mon Sep 17 00:00:00 2001
From: jorgecardleitao <149073281+jorgecardleitao@users.noreply.github.com>
Date: Sun, 28 Jan 2024 11:25:05 +0100
Subject: [PATCH] Improved computation of the leg (#22)

---
 methodology.md | 16 ++++++++--------
 src/legs.rs    | 24 ++++++++++++++++--------
 2 files changed, 24 insertions(+), 16 deletions(-)

diff --git a/methodology.md b/methodology.md
index 66b177c..fb3dc36 100644
--- a/methodology.md
+++ b/methodology.md
@@ -55,16 +55,16 @@ Source code is available at [src/icao_to_trace.rs](./src/icao_to_trace.rs).
 
 ### M-4: Identify legs of a route
 
-This is performed automatically by the computer program. A leg is defined in this methodology has:
+This is performed automatically by the computer program. A leg is defined in this methodology
+has a continuous sequence of ADS-B positions in time where the aircraft is flying.
 
-> a continuous sequence of ADS-B positions split by landings whose distance is higher than 3km and duration longer than 5 minutes
+The aircraft at a given segment between two ADS-B positions is considered grounded (not flying) when either:
+* both positions are on the ground
+* the time between these positions is > 5m and the aircraft is below 10.000 feet
 
-where a landing is identified by either:
-* The previous ADS-B position was flying, and the current is grounded
-* Both the previous and current position is flying, and are separated by more than 5 minutes apart.
-
-The latter condition is used to mitigate the risk that ADS-B radars do not always pick up signals
-too close from the ground, resulting the leg to not be identified.
+The latter condition is used to mitigate the risk that ADS-B receivers sometimes
+do not receive an aircraft's signal when the aircraft is at low altitude.
+When this happens for more than 5m, we consider that the aircraft approached and landed.
 
 Source code is available at [src/legs.rs](./src/legs.rs).
 
diff --git a/src/legs.rs b/src/legs.rs
index 9dc91cd..b7c18dd 100644
--- a/src/legs.rs
+++ b/src/legs.rs
@@ -50,7 +50,19 @@ fn landed(prev_position: &Position, position: &Position) -> bool {
     ) || (matches!(
         (&prev_position, &position),
         (Position::Flying { .. }, Position::Flying { .. })
-    ) && position.datetime() - prev_position.datetime() > time::Duration::minutes(5))
+    ) && position.datetime() - prev_position.datetime() > time::Duration::minutes(5)
+        && position.altitude() < 10000.0)
+}
+
+fn is_grounded(prev_position: &Position, position: &Position) -> bool {
+    matches!(
+        (&prev_position, &position),
+        (Position::Grounded { .. }, Position::Grounded { .. })
+    ) || (matches!(
+        (&prev_position, &position),
+        (Position::Flying { .. }, Position::Flying { .. })
+    ) && position.datetime() - prev_position.datetime() > time::Duration::minutes(5)
+        && position.altitude() < 10000.0)
 }
 
 /// Returns a set of [`Leg`]s from a sequence of [`Position`]s.
@@ -62,13 +74,9 @@ pub fn all_legs(mut positions: impl Iterator<Item = Position>) -> Vec<Leg> {
     let mut sequence: Vec<Position> = vec![];
     let mut legs: Vec<Leg> = vec![];
     positions.for_each(|position| {
-        if let (Position::Grounded { .. }, Position::Grounded { .. }) = (&prev_position, &position)
-        {
-            // legs are by definition the minimum length on ground
-            prev_position = position;
-            return;
-        };
-        sequence.push(position.clone());
+        if !is_grounded(&prev_position, &position) {
+            sequence.push(position.clone());
+        }
         if landed(&prev_position, &position) {
             legs.push(Leg {
                 positions: std::mem::take(&mut sequence),