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Better documentation, and conditional evaluation of derivatives

release/4.3a0
dellaert 2015-07-30 21:55:40 -07:00
parent 2ad50ab86e
commit 91eeede05a
1 changed files with 12 additions and 4 deletions
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16
gtsam/navigation/NavState.cpp
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@ -246,11 +246,11 @@ NavState NavState::update(const Vector3& omega, const Vector3& acceleration,
Matrix39 D_xiP_state;
double dt22 = 0.5 * dt * dt;
dR(xi) << dt * omega;
dP(xi) << dt * bodyVelocity(D_xiP_state) + dt22 * acceleration;
dP(xi) << dt * bodyVelocity(F ? &D_xiP_state : 0) + dt22 * acceleration;
dV(xi) << dt * acceleration;
Matrix9 D_result_xi;
NavState result = retract(xi, F, D_result_xi);
NavState result = retract(xi, F, G1 || G2 ? &D_result_xi : 0);
// Derivative wrt state is computed by retract directly
// However, as dP(xi) also depends on state, we need to add that contribution
@ -259,11 +259,19 @@ NavState NavState::update(const Vector3& omega, const Vector3& acceleration,
}
// derivative wrt omega
if (G1) {
*G1 = dt * D_result_xi.leftCols<3>();
// D_result_dRxi = D_result_xi.leftCols<3>()
// D_dRxi_omega = dt * I_3x3
// *G1 = D_result_omega = D_result_dRxi * D_dRxi_omega
*G1 = D_result_xi.leftCols<3>() * dt;
}
// derivative wrt acceleration
if (G2) {
*G2 = dt22 * D_result_xi.middleCols<3>(3) + dt * D_result_xi.rightCols<3>();
// D_result_dPxi = D_result_xi.middleCols<3>(3)
// D_dPxi_acc = dt22 * I_3x3
// D_result_dVxi = D_result_xi.rightCols<3>()
// D_dVxi_acc = dt * I_3x3
// *G2 = D_result_acc = D_result_dPxi * D_dPxi_acc + D_result_dVxi * D_dVxi_acc
*G2 = D_result_xi.middleCols<3>(3) * dt22 + D_result_xi.rightCols<3>() * dt;
}
return result;
}