double DynamicBody::CalcAtmosphericForce(double dragCoeff) const
{
Body *body = GetFrame()->GetBody();
if (!body || !GetFrame()->IsRotFrame() || !body->IsType(Object::PLANET))
return 0.0;
Planet *planet = static_cast<Planet*>(body);
double dist = GetPosition().Length();
double speed = m_vel.Length();
double pressure, density;
planet->GetAtmosphericState(dist, &pressure, &density);
const double radius = GetClipRadius(); // bogus, preserving behaviour
const double area = radius;
// ^^^ yes that is as stupid as it looks
return 0.5*density*speed*speed*area*dragCoeff;
}
void DynamicBody::CalcExternalForce()
{
// gravity
if (!GetFrame()) return; // no external force if not in a frame
Body *body = GetFrame()->GetBody();
if (body && !body->IsType(Object::SPACESTATION)) { // they ought to have mass though...
vector3d b1b2 = GetPosition();
double m1m2 = GetMass() * body->GetMass();
double invrsqr = 1.0 / b1b2.LengthSqr();
double force = G*m1m2 * invrsqr;
m_externalForce = -b1b2 * sqrt(invrsqr) * force;
}
else m_externalForce = vector3d(0.0);
m_gravityForce = m_externalForce;
// atmospheric drag
if (body && GetFrame()->IsRotFrame() && body->IsType(Object::PLANET))
{
Planet *planet = static_cast<Planet*>(body);
double dist = GetPosition().Length();
double speed = m_vel.Length();
double pressure, density;
planet->GetAtmosphericState(dist, &pressure, &density);
const double radius = GetClipRadius(); // bogus, preserving behaviour
const double AREA = radius;
// ^^^ yes that is as stupid as it looks
const double DRAG_COEFF = 0.1; // 'smooth sphere'
vector3d dragDir = -m_vel.NormalizedSafe();
vector3d fDrag = 0.5*density*speed*speed*AREA*DRAG_COEFF*dragDir;
// make this a bit less daft at high time accel
// only allow atmosForce to increase by .1g per frame
vector3d f1g = m_atmosForce + dragDir * GetMass();
if (fDrag.LengthSqr() > f1g.LengthSqr()) m_atmosForce = f1g;
else m_atmosForce = fDrag;
m_externalForce += m_atmosForce;
}
else m_atmosForce = vector3d(0.0);
// centrifugal and coriolis forces for rotating frames
if (GetFrame()->IsRotFrame()) {
vector3d angRot(0, GetFrame()->GetAngSpeed(), 0);
m_externalForce -= m_mass * angRot.Cross(angRot.Cross(GetPosition())); // centrifugal
m_externalForce -= 2 * m_mass * angRot.Cross(GetVelocity()); // coriolis
}
}
