Change the distance helper program

Given a bug in the C++ code that does the spherical calculations,
flights crossing the dateline had the distance from their route
calculated incorrectly. To work around this, we now pass in an absolute
and relative (percentage of route length) distance into the helper app
and it returns whether the plane position is within that threshold from
the great circle route.

Also, based on some real world examples, I ended up increasing the
threshold percentage from 5% to 10% (NRT-DEN flight right above PDX).

Signed-off-by: Dirk Hohndel <[email protected]>

Author: dirkhh

distance/distance.cpp

@@ -6,44 +6,33 @@
 #include "PolyUtil.hpp"
 
 void usage() {
-    std::cout << "Usage:\n\n\tdistance latP lngP latA lngA [latB lngB]\n\n\tprint the sperical distance of point P from point A or of P from the great circle between A and B\n";
+    std::cout << "Usage:\n\n\tdistance latP lngP latA lngA latB lngB absoluteDelta relativeDelta\n\n\tcheck if a point P is within the given thresholdsa (in meters or percentage of the distance A-B) of the great circle route between A and B.\n";
 }
 
 int main(int argc, char** argv) {
-	if (argc != 5 && argc != 7) {
+	if (argc != 9) {
 		usage();
 		exit(1);
 	}
-	std::string pLat = argv[1];
-	std::string pLng = argv[2];
-	std::string aLat = argv[3];
-	std::string aLng = argv[4];
-
-	LatLng p = { std::stod(pLat), std::stod(pLng) };
-	LatLng a = { std::stod(aLat), std::stod(aLng) };
-
-	std::string bLat, bLng;
-	LatLng b = { 0.0, 0.0 };
+	LatLng p = { std::stod(argv[1]), std::stod(argv[2]) };
+	LatLng a = { std::stod(argv[3]), std::stod(argv[4]) };
+	LatLng b = { std::stod(argv[5]), std::stod(argv[6]) };
+	double distThreshold = std::stod(argv[7]) * 1852;
+	double distPercentage = std::stod(argv[8]);
 
 	double distPA = SphericalUtil::computeDistanceBetween(p, a);
+	double distPB = SphericalUtil::computeDistanceBetween(p, b);
+	double distAB = SphericalUtil::computeDistanceBetween(a, b);
 
-	std::cout << "{\"distPA\": " << distPA / 1852.0;
-
-	if (argc ==7) {
-		std::string bLat = argv[5];
-		std::string bLng = argv[6];
-		LatLng b = { std::stod(bLat), std::stod(bLng) };
+	// calculate if the point is within the given tolerance of the route
+	std::vector<LatLng> route = { a, b};
+	double threshold = std::max(distThreshold, distPercentage * distAB / 100.0);
+	bool withinThreshold = PolyUtil::isLocationOnPath(p, route, threshold);
 
-		double distPB = SphericalUtil::computeDistanceBetween(p, b);
-		std::cout << ",\"distPB\": " << distPB / 1852.0;
-
-		double distAB = SphericalUtil::computeDistanceBetween(a, b);
-		std::cout << ",\"distAB\": " << distAB / 1852.0;
-
-		double distPAB = PolyUtil::distanceToLine(p, a, b);
-		std::cout << ",\"distPAB\": " << distPAB / 1852.0;
-	}
-	std::cout << "}";
+	std::cout << "{\"distPA\": " << distPA / 1852.0;
+	std::cout << ",\"distPB\": " << distPB / 1852.0;
+	std::cout << ",\"distAB\": " << distAB / 1852.0;
+	std::cout << ",\"withinThreshold\": " << withinThreshold << "}";
 
 	return 0;
 }

src/adsb_api/utils/plausible.py

@@ -10,6 +10,7 @@ def plausible(
     airportBLat: str,
     airportBLon: str,
 ):
+    # check if the position is within 50nm or 10% of the total distance of the great circle route
     distanceResult = subprocess.run(
         [
             "/usr/local/bin/distance",
@@ -19,15 +20,11 @@ def plausible(
             airportALon,
             airportBLat,
             airportBLon,
+            "50",
+            "10"
         ],
         capture_output=True,
     )
     distance = orjson.loads(distanceResult.stdout)
-    # lame assumption that the plane should be within
-    # 50nm or 5% or route distance of the great circle route
-    # no concern for direction, no handling of multi segment routes
-    threshold = 50
-    fivePercent = distance["distAB"] / 20
-    if fivePercent > threshold:
-        threshold = fivePercent
-    return distance["distPAB"] < threshold, distance["distAB"]
+    return distance['withinThreshold'], distance['distAB']
+