[Jsbsim-users] issues with propagating dynamics (non-changing longitude)

[Zouhair M. <zou...@gm...>]

I’m trying to use JSBsim to drive an an Xplane visualization (long story as
to why I’m not using FlightGear :p)

I’m not doing anything fancy right now, just want to have a cessna172
model. I tried the snippet of code below, but this is the output I get
(longitude multiploed by 1e6 on purpose)

t = 0.00 , (36.899999, -121404974.000000) IAS = 25.27, theta = 34.52
altMSL = 0.10,
t = 0.00 , (36.900000, -121404974.000000) IAS = 14.94, theta = 3.01
altMSL = 0.67,
t = 0.00 , (36.900001, -121404974.000000) IAS = 17.00, theta = -8.64
altMSL = 1.19,
t = 0.00 , (36.900002, -121404974.000000) IAS = 26.19, theta = -8.57
altMSL = 1.69,
t = 0.00 , (36.900003, -121404974.000000) IAS = 37.59, theta = -3.60
altMSL = 2.17,
t = 0.00 , (36.900004, -121404974.000000) IAS = 49.59, theta = 0.53
altMSL = 2.65,
t = 0.00 , (36.900005, -121404974.000000) IAS = 63.82, theta = 2.34
altMSL = 3.23,
t = 0.00 , (36.900007, -121404974.000000) IAS = 79.51, theta = 2.49
altMSL = 3.92,
t = 0.00 , (36.900009, -121404974.000000) IAS = 96.02, theta = 1.62
altMSL = 4.70,
t = 0.00 , (36.900011, -121404974.000000) IAS = 112.78, theta = 0.37
altMSL = 5.56,

Aside from the time always being 0 (I think this is due to the fact that
I’m using a newer library that doesn’t have sim-time-sec), it looks like
the longitude never changes. I initially thought this might be due to
pointing perfectly north, so I tried initializing with a non-zero heading
but same thing.

I tried using the FGInitialCondition instead of manually setting the
latitude, but just setting
fgic->SetLongitudeDegIC(-121.404974) results in the longitude always
reading 0…

Any help would be most welcome :)

Cheers,

-z

P.S. what's the best source for finding out the most recent PropertyValues ?


Version info:

$uname -a
Linux computer 3.13.0-24-generic #46-Ubuntu SMP Thu Apr 10 19:11:08
UTC 2014 x86_64 x86_64 x86_64 GNU/Linux
$lsb_release -a
No LSB modules are available.
Distributor ID:    Ubuntu
Description:    Ubuntu 14.04 LTS
Release:    14.04
Codename:    trusty

Jsbsim code (from git)
$git show
commit eef1ac615c3d804ceaa947e839e921950e93b486
Merge: ad5e22c ae83b77
Author: bcoconni <bcoconni>
Date:   Fri Sep 12 20:10:04 2014 +0000

Built using:
./autogen.sh --enable-libraries --enable-shared


  FGFDMExec *FDMExec = new FGFDMExec();

  FGFCS* fcs = FDMExec->GetFCS();
  FGPropulsion* prop = FDMExec->GetPropulsion();

  FDMExec->SetAircraftPath("./aircraft");
  FDMExec->SetEnginePath("./engine");
  FDMExec->SetSystemsPath("./systems");
  FDMExec->LoadModel("c172r", true);

//  FGInitialCondition* fgic= FDMExec->GetIC();
//  fgic->SetVcalibratedKtsIC(100);
////  fgic->SetLatitudeDegIC(36.888103);
////  fgic->SetLongitudeDegIC(-121.404974);
////  fgic->SetPsiDegIC(45);
//  fgic->SetAltitudeASLFtIC(1000);
//
//  printf("longitude is : %lf \n", fgic->GetLongitudeDegIC());

  bool result = FDMExec->RunIC();
  FDMExec->SetPropertyValue("position/lon-gc-deg", -121.404974);
  FDMExec->SetPropertyValue("position/lat-gc-deg", 36.9);
  FDMExec->SetPropertyValue("attitude/psi-rad", .1);

  /* run at 100 hz */
  double dt = 1./100;
  FDMExec->Setdt(dt);
  uint64_t dt_usec = (dt * 1e6);
  int counter = 0;
  while(result)
  {
    result = FDMExec->Run();

    if(isnan(FDMExec->GetPropertyValue("position/h-sl-meters")))
    {
      break;
    }
    if(counter++%4 == 1)
    {
  printf("t = %.2lf , (%lf, %lf) IAS = %.2lf, theta = %.2lf altMSL = %.2lf, \n",
         FDMExec->GetPropertyValue("sim-time-sec"),
         FDMExec->GetPropertyValue("position/lat-gc-deg"),
         FDMExec->GetPropertyValue("position/lon-gc-deg")*1000000,

         FDMExec->GetPropertyValue("velocities/u-aero-fps"),
         FDMExec->GetPropertyValue("attitude/theta-rad")*180/3.14,
         FDMExec->GetPropertyValue("position/h-sl-meters"));    }

    usleep(dt_usec); /* sleep for 10 ms */
  }

​