flightgear/src/AIModel/AIAircraft.cxx

// FGAIAircraft - FGAIBase-derived class creates an AI airplane
//
// Written by David Culp, started October 2003.
//
// Copyright (C) 2003  David P. Culp - davidculp2@comcast.net
//
// This program is free software; you can redistribute it and/or
// modify it under the terms of the GNU General Public License as
// published by the Free Software Foundation; either version 2 of the
// License, or (at your option) any later version.
//
// This program is distributed in the hope that it will be useful, but
// WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
// General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program; if not, write to the Free Software
// Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.

#ifdef HAVE_CONFIG_H
#  include <config.h>
#endif

#include <simgear/math/point3d.hxx>
#include <Main/fg_props.hxx>
#include <Main/globals.hxx>
#include <Scenery/scenery.hxx>
#include <string>
#include <math.h>

SG_USING_STD(string);

#include "AIAircraft.hxx"


const FGAIAircraft::PERF_STRUCT FGAIAircraft::settings[] = {
    // light aircraft
    {2.0, 2.0,  450.0, 1000.0,  70.0,  80.0, 100.0,  80.0,  60.0},
    // ww2_fighter
    {4.0, 2.0, 3000.0, 1500.0, 110.0, 180.0, 250.0, 200.0, 100.0},
    // jet_transport
    {5.0, 2.0, 3000.0, 1500.0, 140.0, 300.0, 430.0, 300.0, 130.0},
    // jet_fighter
    {7.0, 3.0, 4000.0, 2000.0, 150.0, 350.0, 500.0, 350.0, 150.0}
};


FGAIAircraft::FGAIAircraft() {

   // set heading and altitude locks
   hdg_lock = false;
   alt_lock = false;
   _type_str = "aircraft";
}


FGAIAircraft::~FGAIAircraft() {
}


bool FGAIAircraft::init() {
   return FGAIBase::init();
}

void FGAIAircraft::bind() {
    FGAIBase::bind();
}

void FGAIAircraft::unbind() {
    FGAIBase::unbind();
}


void FGAIAircraft::update(double dt) {

   Run(dt);
   Transform();
   FGAIBase::update(dt);
}

void FGAIAircraft::SetPerformance(const PERF_STRUCT *ps) {
   
   performance = ps;
} 


void FGAIAircraft::Run(double dt) {

   FGAIAircraft::dt = dt;
	
   double turn_radius_ft;
   double turn_circum_ft;
   double speed_north_deg_sec;
   double speed_east_deg_sec;
   double ft_per_deg_lon;
   double ft_per_deg_lat;
   double dist_covered_ft;
   double alpha;

   // get size of a degree at this latitude
   ft_per_deg_lat = 366468.96 - 3717.12 * cos(pos.lat()/SG_RADIANS_TO_DEGREES);
   ft_per_deg_lon = 365228.16 * cos(pos.lat() / SG_RADIANS_TO_DEGREES);

   // adjust speed
   double speed_diff = tgt_speed - speed;
   if (fabs(speed_diff) > 0.2) {
     if (speed_diff > 0.0) speed += performance->accel * dt;
     if (speed_diff < 0.0) speed -= performance->decel * dt;
   } 
   
   // convert speed to degrees per second
   speed_north_deg_sec = cos( hdg / SG_RADIANS_TO_DEGREES )
                          * speed * 1.686 / ft_per_deg_lat;
   speed_east_deg_sec  = sin( hdg / SG_RADIANS_TO_DEGREES )
                          * speed * 1.686 / ft_per_deg_lon;

   // set new position
   pos.setlat( pos.lat() + speed_north_deg_sec * dt);
   pos.setlon( pos.lon() + speed_east_deg_sec * dt); 

   // adjust heading based on current bank angle
   if (roll != 0.0) {
     turn_radius_ft = 0.088362 * speed * speed
                       / tan( fabs(roll) / SG_RADIANS_TO_DEGREES );
     turn_circum_ft = SGD_2PI * turn_radius_ft;
     dist_covered_ft = speed * 1.686 * dt; 
     alpha = dist_covered_ft / turn_circum_ft * 360.0;
     hdg += alpha * sign( roll );
     if ( hdg > 360.0 ) hdg -= 360.0;
     if ( hdg < 0.0) hdg += 360.0;
   }

   // adjust target bank angle if heading lock engaged
   if (hdg_lock) {
     double bank_sense = 0.0;
     double diff = fabs(hdg - tgt_heading);
     if (diff > 180) diff = fabs(diff - 360);
     double sum = hdg + diff;
     if (sum > 360.0) sum -= 360.0;
     if (fabs(sum - tgt_heading) < 1.0) { 
       bank_sense = 1.0;
     } else {
       bank_sense = -1.0;
     } 
     if (diff < 30) tgt_roll = diff * bank_sense; 
   }

   // adjust bank angle
   double bank_diff = tgt_roll - roll;
   if (fabs(bank_diff) > 0.2) {
     if (bank_diff > 0.0) roll += 5.0 * dt;
     if (bank_diff < 0.0) roll -= 5.0 * dt;
   }

   // adjust altitude (meters) based on current vertical speed (fpm)
   altitude += vs * 0.0166667 * dt * SG_FEET_TO_METER;  

   // find target vertical speed if altitude lock engaged
   if (alt_lock) {
     double altitude_ft = altitude * SG_METER_TO_FEET;
     if (altitude_ft < tgt_altitude) {
       tgt_vs = tgt_altitude - altitude_ft;
       if (tgt_vs > performance->climb_rate)
         tgt_vs = performance->climb_rate;
     } else {
       tgt_vs = tgt_altitude - altitude_ft;
       if (tgt_vs  < (-performance->descent_rate))
         tgt_vs = -performance->descent_rate;
     }
   }

   // adjust vertical speed
   double vs_diff = tgt_vs - vs;
   if (fabs(vs_diff) > 1.0) {
     if (vs_diff > 0.0) {
       vs += 400.0 * dt;
       if (vs > tgt_vs) vs = tgt_vs;
     } else {
       vs -= 300.0 * dt;
       if (vs < tgt_vs) vs = tgt_vs;
     }
   }   
   
   // match pitch angle to vertical speed
   pitch = vs * 0.005;

}


void FGAIAircraft::AccelTo(double speed) {
   tgt_speed = speed;
}


void FGAIAircraft::PitchTo(double angle) {
   tgt_pitch = angle;
   alt_lock = false;
}


void FGAIAircraft::RollTo(double angle) {
   tgt_roll = angle;
   hdg_lock = false; 
}


void FGAIAircraft::YawTo(double angle) {
   tgt_yaw = angle;
}


void FGAIAircraft::ClimbTo(double altitude) {
   tgt_altitude = altitude;
   alt_lock = true;
}


void FGAIAircraft::TurnTo(double heading) {
   tgt_heading = heading;
   hdg_lock = true;
}


double FGAIAircraft::sign(double x) {

  if ( x < 0.0 ) { return -1.0; }
  else { return 1.0; }
}