From acdbf9d43db81c0aa7ba821c6a561edbd264d8fe Mon Sep 17 00:00:00 2001
From: Mat Sutcliffe <oktal3700@gmail.com>
Date: Sun, 16 Dec 2018 20:43:53 +0000
Subject: [PATCH] Ref T470 CTraffic::getRemoteAircraftData uses NaN to
 represent an unknown vertical offset.

---
 src/xswiftbus/traffic.cpp | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/src/xswiftbus/traffic.cpp b/src/xswiftbus/traffic.cpp
index 889f3bca3..3814c4ea1 100644
--- a/src/xswiftbus/traffic.cpp
+++ b/src/xswiftbus/traffic.cpp
@@ -26,6 +26,7 @@
 #include <cmath>
 #include <ctime>
 #include <algorithm>
+#include <limits>
 
 // clazy:excludeall=reserve-candidates
 
@@ -441,13 +442,13 @@ namespace XSwiftBus
             double groundElevation = plane->terrainProbe.getElevation(latDeg, lonDeg, plane->position.elevation);
             if (std::isnan(groundElevation)) { groundElevation = 0.0; }
             double fudgeFactor = 3.0;
-            XPMPGetVerticalOffset(plane->id, &fudgeFactor);
+            bool hasOffset = XPMPGetVerticalOffset(plane->id, &fudgeFactor);
 
             callsigns.push_back(requestedCallsign);
             latitudesDeg.push_back(latDeg);
             longitudesDeg.push_back(lonDeg);
             elevationsM.push_back(groundElevation);
-            verticalOffsets.push_back(fudgeFactor);
+            verticalOffsets.push_back(hasOffset ? fudgeFactor : std::numeric_limits<decltype(fudgeFactor)>::quiet_NaN());
         }
     }