Unverified Commit b4be6e0d authored by Oleg Alexandrov's avatar Oleg Alexandrov Committed by GitHub
Browse files

SAR model: Fix an infinite loop issue (#382) 

* SAR model: Fix an infinite loop issue

* Add note that convergence may not be in one step for a nonspherical datum
parent 41152a2b

src/UsgsAstroSarSensorModel.cpp

+10 −3
Original line number Diff line number Diff line
@@ -524,12 +524,16 @@ csm::EcefCoord UsgsAstroSarSensorModel::imageToGround( 
  //   The cross-track unit vector is orthogonal to the position so we ignore it

  double nadirComp = dot(spacecraftPosition, tHat);



  // Iterate to find proper radius value

  // Iterate to find proper radius value. Limit the number of iterations

  // because the desired precision may not drop beyond 1e-10 no matter

  // how many iterations one does. As it was observed, this in fact

  // converges at the first iteration; this is expected for a spherical

  // datum and not for an ellipsoidal one.

  double pointRadius = m_majorAxis + height;

  double radiusSqr;

  double pointHeight;

  csm::EcefVector groundVec;

  do {

  for (int it = 0; it < 10; it++) {

    radiusSqr = pointRadius * pointRadius;

    double alpha =

        (radiusSqr - slantRange * slantRange - positionMag * positionMag) /
@@ -542,7 +546,10 @@ csm::EcefCoord UsgsAstroSarSensorModel::imageToGround( 
    pointHeight = computeEllipsoidElevation(

        groundVec.x, groundVec.y, groundVec.z, m_majorAxis, m_minorAxis);

    pointRadius -= (pointHeight - height);

  } while (fabs(pointHeight - height) > desiredPrecision);



    if (fabs(pointHeight - height) <= desiredPrecision)

      break;

  }



  if (achievedPrecision) {

    *achievedPrecision = fabs(pointHeight - height);