flightgear/src/AIModel/AIBallistic.cxx

// FGAIBallistic - FGAIBase-derived class creates a ballistic object
//
// Written by David Culp, started November 2003.
// - davidculp2@comcast.net
//
// With major additions by Mathias Froehlich & Vivian Meazza 2004-2007
//
// 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., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.

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

#include <simgear/math/point3d.hxx>
#include <simgear/math/sg_random.h>
#include <math.h>

#include "AIBallistic.hxx"


FGAIBallistic::FGAIBallistic() : FGAIBase(otBallistic) {
    drag_area = 0.007;
    life_timer = 0.0;
    gravity = 32;
//  buoyancy = 64;
    no_roll = false;
    aero_stabilised = false;
}

FGAIBallistic::~FGAIBallistic() {
}

void FGAIBallistic::readFromScenario(SGPropertyNode* scFileNode) {
  if (!scFileNode)
    return;

  FGAIBase::readFromScenario(scFileNode);

  setAzimuth(scFileNode->getDoubleValue("azimuth", 0.0));
  setElevation(scFileNode->getDoubleValue("elevation", 0.0));
  setDragArea(scFileNode->getDoubleValue("eda", 0.007));
  setLife(scFileNode->getDoubleValue("life", 900.0));
  setBuoyancy(scFileNode->getDoubleValue("buoyancy", 0));
  setWind_from_east(scFileNode->getDoubleValue("wind_from_east", 0));
  setWind_from_north(scFileNode->getDoubleValue("wind_from_north", 0));
  setWind(scFileNode->getBoolValue("wind", false));
  setRoll(scFileNode->getDoubleValue("roll", 0.0));
  setCd(scFileNode->getDoubleValue("cd", 0.029));
  setMass(scFileNode->getDoubleValue("mass", 0.007));
  setStabilisation(scFileNode->getBoolValue("aero_stabilized", false));
  setNoRoll(scFileNode->getBoolValue("no-roll", false));
  setRandom(scFileNode->getBoolValue("random", false));
}

bool FGAIBallistic::init(bool search_in_AI_path) {
   FGAIBase::init(search_in_AI_path);
   hdg = azimuth;
   pitch = elevation;
   roll = rotation;
   Transform();
   return true;
}

void FGAIBallistic::bind() {
//    FGAIBase::bind();
   props->tie("sim/time/elapsed-sec",
               SGRawValueMethods<FGAIBallistic,double>(*this,
                                          &FGAIBallistic::_getTime));
}

void FGAIBallistic::unbind() {
//    FGAIBase::unbind();
   props->untie("sim/time/elapsed-sec");
}

void FGAIBallistic::update(double dt) {
   FGAIBase::update(dt);
   Run(dt);
   Transform();
}

void FGAIBallistic::setAzimuth(double az) {
   hdg = azimuth = az;
}

void FGAIBallistic::setElevation(double el) {
   pitch = elevation = el;
}

void FGAIBallistic::setRoll(double rl) {
   rotation = rl;
}

void FGAIBallistic::setStabilisation(bool val) {
   aero_stabilised = val;
}

void FGAIBallistic::setNoRoll(bool nr) {
    no_roll = nr;
}

void FGAIBallistic::setDragArea(double a) {
   drag_area = a;
}

void FGAIBallistic::setLife(double seconds) {
   life = seconds;
}

void FGAIBallistic::setBuoyancy(double fpss) {
   buoyancy = fpss;
}

void FGAIBallistic::setWind_from_east(double fps) {
   wind_from_east = fps;
}

void FGAIBallistic::setWind_from_north(double fps) {
   wind_from_north = fps;
}

void FGAIBallistic::setWind(bool val) {
   wind = val;
}

void FGAIBallistic::setCd(double c) {
   Cd = c;
}

void FGAIBallistic::setMass(double m) {
   mass = m;
}

void FGAIBallistic::setRandom(bool r) {
    random = r;
}

void FGAIBallistic::setName(const string& n) {
    name = n;
}

void FGAIBallistic::Run(double dt) {
   life_timer += dt;
//    cout << "life timer 1" << life_timer <<  dt << endl;
   if (life_timer > life) setDie(true); 

   double speed_north_deg_sec;
   double speed_east_deg_sec;
   double wind_speed_from_north_deg_sec;
   double wind_speed_from_east_deg_sec;
   double Cdm;      // Cd adjusted by Mach Number
   
    //randomise Cd by +- 5%
    if (random)
        Cd = Cd * 0.95 + (0.05 * sg_random());

   // Adjust Cd by Mach number. The equations are based on curves
   // for a conventional shell/bullet (no boat-tail). 
    if ( Mach < 0.7 )
        Cdm = 0.0125 * Mach + Cd;
    else if ( 0.7 < Mach && Mach < 1.2 )
        Cdm = 0.3742 * pow ( Mach, 2) - 0.252 * Mach + 0.0021 + Cd;
    else
        Cdm = 0.2965 * pow ( Mach, -1.1506 ) + Cd;

    //cout << " Mach , " << Mach << " , Cdm , " << Cdm << " ballistic speed kts //"<< speed <<  endl;
   
   // drag = Cd * 0.5 * rho * speed * speed * drag_area;
   // rho is adjusted for altitude in void FGAIBase::update,
   // using Standard Atmosphere (sealevel temperature 15C)
   // acceleration = drag/mass;
   // adjust speed by drag
   speed -= (Cdm * 0.5 * rho * speed * speed * drag_area/mass) * dt; 

   // don't let speed become negative
    if ( speed < 0.0 )
        speed = 0.0;

    double speed_fps = speed * SG_KT_TO_FPS;
   
   // calculate vertical and horizontal speed components
    vs = sin( pitch * SG_DEGREES_TO_RADIANS ) * speed_fps;
    double hs = cos( pitch * SG_DEGREES_TO_RADIANS ) * speed_fps;

   // convert horizontal speed (fps) to degrees per second
   speed_north_deg_sec = cos(hdg / SG_RADIANS_TO_DEGREES) * hs / ft_per_deg_lat;
   speed_east_deg_sec  = sin(hdg / SG_RADIANS_TO_DEGREES) * hs / ft_per_deg_lon;
   
   // if wind not required, set to zero
   if (!wind) {
      wind_from_north = 0;
      wind_from_east = 0;
   }
  
   // convert wind speed (fps) to degrees per second
   wind_speed_from_north_deg_sec = wind_from_north / ft_per_deg_lat;
   wind_speed_from_east_deg_sec  = wind_from_east / ft_per_deg_lon;
   
   // set new position
    pos.setLatitudeDeg( pos.getLatitudeDeg()
        + (speed_north_deg_sec - wind_speed_from_north_deg_sec) * dt );
    pos.setLongitudeDeg( pos.getLongitudeDeg()
        + (speed_east_deg_sec - wind_speed_from_east_deg_sec) * dt );

   // adjust vertical speed for acceleration of gravity and buoyancy
   vs -= (gravity - buoyancy) * dt;
   
   // adjust altitude (feet)
   altitude_ft += vs * dt;
   pos.setElevationFt(altitude_ft); 

   // recalculate pitch (velocity vector) if aerostabilized
    /*cout << name << ": " << "aero_stabilised " << aero_stabilised
    << " pitch " << pitch <<" vs "  << vs <<endl ;*/

    if (aero_stabilised)
        pitch = atan2( vs, hs ) * SG_RADIANS_TO_DEGREES;

   // recalculate total speed
    speed = sqrt( vs * vs + hs * hs) / SG_KT_TO_FPS;

   // set destruction flag if altitude less than sea level -1000
   if (altitude_ft < -1000.0) setDie(true);

}  // end Run

double FGAIBallistic::_getTime() const {
//    cout << "life timer 2" << life_timer << endl;
  return life_timer;
}

// end AIBallistic