David Culp:

Here are files to get automated contrails working.  I've set up contrails for
the 737, using my simple, untextured contrail model.  Vivian has made another
contrail model, but I'm still trying to get his to work.  I'm hoping others
will try to make contrail models also.

Here's some code that defines a top to thermals.  When the top of a thermal is
reached the strength is phased-out linearly over the next 100 feet of
altitude.  At first I tried just capping the thermal at the top, but the
change in thermal strength was too fast for the FDM to handle well.

Included is a new version of the thermal scenario that includes a top
(height-msl) to the thermal.  The default value is 5000 feet.

src/AIModel/AIBase.hxx

@@ -57,6 +57,7 @@ typedef struct {
    double rudder;             // used by ship objects
    double strength;           // used by thermal objects
    double diameter;           // used by thermal objects
+   double height_msl;         // used by thermal objects
    double eda;                // used by ballistic objects
    double life;               // life span in seconds
    double buoyancy;           // acceleration in ft per sec2

src/AIModel/AIScenario.cxx

@@ -74,6 +74,7 @@ FGAIScenario::FGAIScenario(string &filename)
      en->rudder         = entry_node->getDoubleValue("rudder", 0.0);
      en->strength       = entry_node->getDoubleValue("strength-fps", 0.0);
      en->diameter       = entry_node->getDoubleValue("diameter-ft", 0.0);
+     en->height_msl     = entry_node->getDoubleValue("height-msl", 5000.0);
      en->eda            = entry_node->getDoubleValue("eda", 0.007);
      en->life           = entry_node->getDoubleValue("life", 900.0);
      en->buoyancy       = entry_node->getDoubleValue("buoyancy", 0);

src/AIModel/AIThermal.cxx

@@ -80,7 +80,7 @@ void FGAIThermal::Run(double dt) {
    // copy values from the AIManager
    double user_latitude  = manager->get_user_latitude();
    double user_longitude = manager->get_user_longitude();
-   // double user_altitude  = manager->get_user_altitude();
+   double user_altitude  = manager->get_user_altitude();
 
    // calculate range to target in feet and nautical miles
    double lat_range = fabs(pos.lat() - user_latitude) * ft_per_deg_lat;
@@ -96,5 +96,16 @@ void FGAIThermal::Run(double dt) {
    } else {
      strength = 0.0;
    }
+
+   // Stop lift at the top of the thermal (smoothly)
+   if (user_altitude > (height + 100.0)) {
+     strength = 0.0;
+   }
+   else if (user_altitude < height) {
+     // do nothing
+   }
+   else {
+     strength -= (strength * (user_altitude - height) * 0.01);
+   }
 }
 

src/AIModel/AIThermal.hxx

@@ -42,8 +42,10 @@ public:
 
         inline void setMaxStrength( double s ) { max_strength = s; };
         inline void setDiameter( double d ) { diameter = d; };
+        inline void setHeight( double h ) { height = h; };
         inline double getStrength() const { return strength; };
         inline double getDiameter() const { return diameter; };
+        inline double getHeight() const { return height; };
 
 private:
 
@@ -52,6 +54,7 @@ private:
         double max_strength;
         double strength;
         double diameter;
+        double height;
         double factor;
 };
 

src/AIModel/submodel.cxx

@@ -26,6 +26,7 @@ FGSubmodelMgr::FGSubmodelMgr ()
   out[0] = out[1] = out[2] = 0;
   in[3] = out[3] = 1;
   string contents_node;
+  contrail_altitude = 30000.0;
 }
 
 FGSubmodelMgr::~FGSubmodelMgr ()
@@ -57,8 +58,12 @@ FGSubmodelMgr::init ()
     _user_speed_east_fps_node   = fgGetNode("/velocities/speed-east-fps",true);
     _user_speed_north_fps_node  = fgGetNode("/velocities/speed-north-fps",true);
 
-    ai = (FGAIManager*)globals->get_subsystem("ai_model");
+    _contrail_altitude_node = fgGetNode("/environment/params/contrail-altitude", true);
+    contrail_altitude = _contrail_altitude_node->getDoubleValue();
+    _contrail_trigger = fgGetNode("ai/submodels/contrails", true);
+    _contrail_trigger->setBoolValue(false);
 
+    ai = (FGAIManager*)globals->get_subsystem("ai_model");
 
 }
 
@@ -82,6 +87,11 @@ FGSubmodelMgr::update (double dt)
 {
   if (!(_serviceable_node->getBoolValue())) return;
   int i=-1;
+
+  if (_user_alt_node->getDoubleValue() > contrail_altitude) {
+     _contrail_trigger->setBoolValue(true);
+  }   
+
   submodel_iterator = submodels.begin();
   while(submodel_iterator != submodels.end()) {
     i++;

src/AIModel/submodel.hxx

@@ -114,6 +114,8 @@ private:
 
     static const double lbs_to_slugs; //conversion factor
 
+    double contrail_altitude;
+
     SGPropertyNode* _serviceable_node;
     SGPropertyNode* _user_lat_node;
     SGPropertyNode* _user_lon_node;
@@ -129,6 +131,8 @@ private:
     SGPropertyNode* _user_speed_down_fps_node;
     SGPropertyNode* _user_speed_east_fps_node;
     SGPropertyNode* _user_speed_north_fps_node;
+    SGPropertyNode* _contrail_altitude_node;
+    SGPropertyNode* _contrail_trigger;
 
     FGAIManager* ai;
     IC_struct  IC;