1 /*******************************************************************************
6 Purpose: Integrate the EOM to determine instantaneous position
9 ------------- Copyright (C) 1999 Jon S. Berndt (jsb@hal-pc.org) -------------
11 This program is free software; you can redistribute it and/or modify it under
12 the terms of the GNU General Public License as published by the Free Software
13 Foundation; either version 2 of the License, or (at your option) any later
16 This program is distributed in the hope that it will be useful, but WITHOUT
17 ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
18 FOR A PARTICULAR PURPOSE. See the GNU General Public License for more
21 You should have received a copy of the GNU General Public License along with
22 this program; if not, write to the Free Software Foundation, Inc., 59 Temple
23 Place - Suite 330, Boston, MA 02111-1307, USA.
25 Further information about the GNU General Public License can also be found on
26 the world wide web at http://www.gnu.org.
28 FUNCTIONAL DESCRIPTION
29 --------------------------------------------------------------------------------
30 This class encapsulates the integration of rates and accelerations to get the
31 current position of the aircraft.
34 --------------------------------------------------------------------------------
38 --------------------------------------------------------------------------------
41 ********************************************************************************
42 COMMENTS, REFERENCES, and NOTES
43 ********************************************************************************
44 [1] Cooke, Zyda, Pratt, and McGhee, "NPSNET: Flight Simulation Dynamic Modeling
45 Using Quaternions", Presence, Vol. 1, No. 4, pp. 404-420 Naval Postgraduate
47 [2] D. M. Henderson, "Euler Angles, Quaternions, and Transformation Matrices",
49 [3] Richard E. McFarland, "A Standard Kinematic Model for Flight Simulation at
50 NASA-Ames", NASA CR-2497, January 1975
51 [4] Barnes W. McCormick, "Aerodynamics, Aeronautics, and Flight Mechanics",
52 Wiley & Sons, 1979 ISBN 0-471-03032-5
53 [5] Bernard Etkin, "Dynamics of Flight, Stability and Control", Wiley & Sons,
54 1982 ISBN 0-471-08936-2
56 ********************************************************************************
58 *******************************************************************************/
60 #include "FGPosition.h"
63 /*******************************************************************************
64 ************************************ CODE **************************************
65 *******************************************************************************/
68 FGPosition::FGPosition(void) : FGModel()
70 strcpy(Name, "FGPosition");
71 EarthRad = 20898908.00; // feet
72 OmegaEarth = 7.2685E-3; // rad/sec
73 AccelN = AccelE = AccelD = 0.0;
74 LongitudeDot = LatitudeDot = RadiusDot = 0.0;
78 FGPosition::~FGPosition(void)
83 bool FGPosition:: Run(void)
87 if (!FGModel::Run()) {
89 T[1][1] = Q0*Q0 + Q1*Q1 - Q2*Q2 - Q3*Q3; // Page A-11
90 T[1][2] = 2*(Q1*Q2 + Q0*Q3); // From
91 T[1][3] = 2*(Q1*Q3 - Q0*Q2); // Reference [2]
92 T[2][1] = 2*(Q1*Q2 - Q0*Q3);
93 T[2][2] = Q0*Q0 - Q1*Q1 + Q2*Q2 - Q3*Q3;
94 T[2][3] = 2*(Q2*Q3 + Q0*Q1);
95 T[3][1] = 2*(Q1*Q3 + Q0*Q2);
96 T[3][2] = 2*(Q2*Q3 - Q0*Q1);
97 T[3][3] = Q0*Q0 - Q1*Q1 - Q2*Q2 + Q3*Q3;
99 Fn = T[1][1]*Fx + T[2][1]*Fy + T[3][1]*Fz; // Eqn. 3.5
100 Fe = T[1][2]*Fx + T[2][2]*Fy + T[3][2]*Fz; // From
101 Fd = T[1][3]*Fx + T[2][3]*Fy + T[3][3]*Fz; // Reference [3]
103 tanLat = tan(Latitude); // I made this up
104 cosLat = cos(Latitude);
110 Vn = T[1][1]*U + T[2][1]*V + T[3][1]*W;
111 Ve = T[1][2]*U + T[2][2]*V + T[3][2]*W;
112 Vd = T[1][3]*U + T[2][3]*V + T[3][3]*W;
114 AccelN = invMass * Fn + invRadius * (Vn*Vd - Ve*Ve*tanLat); // Eqn. 3.6
115 AccelE = invMass * Fe + invRadius * (Ve*Vd + Vn*Ve*tanLat); // From
116 AccelD = invMass * Fd - invRadius * (Vn*Vn + Ve*Ve); // Reference [3]
118 Vn += 0.5*dt*(3.0*AccelN - lastAccelN); // Eqn. 3.7
119 Ve += 0.5*dt*(3.0*AccelE - lastAccelE); // From
120 Vd += 0.5*dt*(3.0*AccelD - lastAccelD); // Reference [3]
122 Vee = Ve - OmegaEarth * (Radius) * cosLat; // From Eq. 3.8
124 lastLatitudeDot = LatitudeDot;
125 lastLongitudeDot = LongitudeDot;
126 lastRadiusDot = RadiusDot;
128 if (cosLat != 0) LongitudeDot = Ve / (Radius * cosLat);
129 LatitudeDot = Vn * invRadius;
132 Longitude += 0.5*dt*(LongitudeDot + lastLongitudeDot);
133 Latitude += 0.5*dt*(LatitudeDot + lastLatitudeDot);
134 Radius += 0.5*dt*(RadiusDot + lastRadiusDot);
144 void FGPosition::GetState(void)
159 Latitude = State->Getlatitude();
160 Longitude = State->Getlongitude();
162 invMass = 1.0 / State->Getm();
163 invRadius = 1.0 / (State->Geth() + EarthRad);
164 Radius = State->Geth() + EarthRad;
169 void FGPosition::PutState(void)
171 for (int r=1;r<=3;r++)
172 for (int c=1;c<=3;c++)
173 State->SetT(r,c,T[r][c]);
175 State->Setlatitude(Latitude);
176 State->Setlongitude(Longitude);
177 State->Seth(Radius - EarthRad);
179 State->SetVn(Vn); // remove after testing
180 State->SetVe(Ve); // remove after testing
181 State->SetVd(Vd); // remove after testing