Encapsulate the interpolstion version of FGEnvironment and fix some bugs

[flightgear.git] / src / FDM / JSBSim / FGMassBalance.cpp

diff --git a/src/FDM/JSBSim/FGMassBalance.cpp b/src/FDM/JSBSim/FGMassBalance.cpp
index ab9b725d49dc86bfb05d9d1ebb1c8126964cc57d..582f1d957dc5e7e7991615a5a6930be77bbf4d60 100644 (file)
--- a/src/FDM/JSBSim/FGMassBalance.cpp
+++ b/src/FDM/JSBSim/FGMassBalance.cpp
@@ -198,6 +198,39 @@ double FGMassBalance::GetPMIxz(void)
 
 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 
+FGColumnVector3 FGMassBalance::StructuralToBody(const FGColumnVector3& r) const
+{
+  // Under the assumption that in the structural frame the:
+  //
+  // - X-axis is directed afterwards,
+  // - Y-axis is directed towards the right,
+  // - Z-axis is directed upwards,
+  //
+  // (as documented in http://jsbsim.sourceforge.net/JSBSimCoordinates.pdf)
+  // we have to subtract first the center of gravity of the plane which
+  // is also defined in the structural frame:
+  //
+  //   FGColumnVector3 cgOff = r - vXYZcg;
+  //
+  // Next, we do a change of units:
+  //
+  //   cgOff *= inchtoft;
+  //
+  // And then a 180 degree rotation is done about the Y axis so that the:
+  //
+  // - X-axis is directed forward,
+  // - Y-axis is directed towards the right,
+  // - Z-axis is directed downward.
+  //
+  // This is needed because the structural and body frames are 180 degrees apart.
+
+  return FGColumnVector3(inchtoft*(vXYZcg(1)-r(1)),
+                         inchtoft*(r(2)-vXYZcg(2)),
+                         inchtoft*(vXYZcg(3)-r(3)));
+}
+
+//%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+
 void FGMassBalance::bind(void)
 { 
   typedef double (FGMassBalance::*PMF)(int) const;