Freeze individual parameters

[Jaznos]

Hello!
is there any idea of how to freeze single parameter like the heading or the pitch? i know that there is a sort of position freeze and attitude freeze implimented that consiste of avoiding the integration of the angular and linear positions and rates
thanks!

[seanmcleod]

I'm not aware of any ability to freeze individual state.

Maybe you're thinking of SuspendIntegration()? Although it's not specific to position and attitude. It's used by code like the trim code etc.

jsbsim/src/FGFDMExec.h

Lines 554 to 555 in 56c6662

	/// Suspends the simulation and sets the delta T to zero.
	void SuspendIntegration(void) {saved_dT = dT; dT = 0.0;}

There is also a hold option, but again it's global.

jsbsim/src/FGFDMExec.h

Lines 487 to 488 in 56c6662

	/// Pauses execution by preventing time from incrementing.
	void Hold(void) {holding = true;}

[Jaznos]

i am talking about this part on FGPropagate.cpp
using eNone as integrator_rotational_position and integrator_rotational_rate to freeze attitude
and integrator_translational_position and integrator_translational_rate to freeze position

 if (!FDMExec->IntegrationSuspended()) {
    Integrate(VState.qAttitudeECI,      VState.vQtrndot,      VState.dqQtrndot,          dt, integrator_rotational_position);
    Integrate(VState.vPQRi,             in.vPQRidot,          VState.dqPQRidot,          dt, integrator_rotational_rate);
    Integrate(VState.vInertialPosition, VState.vInertialVelocity, VState.dqInertialVelocity, dt, integrator_translational_position);
    Integrate(VState.vInertialVelocity, in.vUVWidot,          VState.dqUVWidot,          dt, integrator_translational_rate);
  }

[Jaznos]

i think that the probleme is that the integration s are done in the inertial frame
if we were on the local frame we have juste to set the same value each iteration for exemple give the same value to the heading each iteration
VState.qAttitudeLocal(Psi) =same value.

[bcoconni]

As you mentioned JSBSim is not able to freeze an individual parameter and there are currently no plans to do so. Also note that this kind of feature may not result in what most people are expecting: for example, freezing the heading in the local frame does not result in the aircraft flying along a geodesic (i.e. a "straight" line) unless its heading is exactly 0, 90, 180 or 270 degrees.