From 1f73cf7f8aa85e0bb65db8119f9d1b892a1675f2 Mon Sep 17 00:00:00 2001
From: Sean McLeod <sean@seanmcleod.com>
Date: Sun, 30 Jun 2024 23:23:37 +0200
Subject: [PATCH] Add unit to AGL property name, comment for AGL member,
 prevent negative AGL value

---
 src/models/FGLGear.cpp | 8 +++++---
 src/models/FGLGear.h   | 4 ++--
 2 files changed, 7 insertions(+), 5 deletions(-)

diff --git a/src/models/FGLGear.cpp b/src/models/FGLGear.cpp
index abd51e0f5..d9aae6a6d 100644
--- a/src/models/FGLGear.cpp
+++ b/src/models/FGLGear.cpp
@@ -293,11 +293,13 @@ const FGColumnVector3& FGLGear::GetBodyForces(void)
   gearLoc = in.Location.LocalToLocation(vLocalGear);
 
   // Compute the height of the theoretical location of the wheel (if strut is
-  // not compressed) with respect to the ground level
+  // not compressed) with respect to the ground level (AGL)
   double height = fdmex->GetInertial()->GetContactPoint(gearLoc, contact,
     normal, terrainVel, dummy);
 
-  AGL = height;
+  // Don't want strut compression when in contact with the ground to return 
+  // a negative AGL
+  AGL = max(height, 0.0);
 
   if (isRetractable) gearPos = GetGearUnitPos();
 
@@ -788,7 +790,7 @@ void FGLGear::bind(FGPropertyManager* PropertyManager)
     return;
   }
 
-  property_name = base_property_name + "/AGL";
+  property_name = base_property_name + "/AGL-ft";
   PropertyManager->Tie(property_name.c_str(), &AGL);
   property_name = base_property_name + "/WOW";
   PropertyManager->Tie( property_name.c_str(), &WOW );
diff --git a/src/models/FGLGear.h b/src/models/FGLGear.h
index 0fcbb5607..b35c2c36f 100644
--- a/src/models/FGLGear.h
+++ b/src/models/FGLGear.h
@@ -355,7 +355,7 @@ class JSBSIM_API FGLGear : public FGForce
   double maximumForce = DBL_MAX;
   double bumpiness = 0.0;
   bool isSolid = true;
-  bool WOW;
+  bool WOW; // Weight On Wheel
   bool lastWOW;
   bool FirstContact;
   bool StartedGroundRun;
@@ -366,7 +366,7 @@ class JSBSIM_API FGLGear : public FGForce
   bool Castered;
   bool StaticFriction;
   std::string name;
-  double AGL;
+  double AGL; // Height above ground level
 
   BrakeGroup  eBrakeGrp;
   ContactType eContactType;