IMU Data Problem

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Hi,

I have a gyro - no accelerometer or compass so only generating orientation IMU data. I'm getting a problem with Google's cartographer where is dies with an error:

[FATAL] [1478971675.576678386]: F1112 17:27:55.000000  2963 imu_tracker.cc:70] Check failed: (orientation_ * gravity_vector_).z() > 0. (nan vs. 0)

From the code this is coming from the Linear Acceleration checks:

void ImuTracker::AddImuLinearAccelerationObservation(
 const Eigen::Vector3d& imu_linear_acceleration) {
 // Update the 'gravity_vector_' with an exponential moving average using the
 // 'imu_gravity_time_constant'.
 const double delta_t =
  last_linear_acceleration_time_ > common::Time::min()
      ? common::ToSeconds(time_ - last_linear_acceleration_time_)
      : std::numeric_limits<double>::infinity();
  last_linear_acceleration_time_ = time_;
  const double alpha = 1. - std::exp(-delta_t / imu_gravity_time_constant_);
 gravity_vector_ =
     (1. - alpha) * gravity_vector_ + alpha * imu_linear_acceleration;
 // Change the 'orientation_' so that it agrees with the current
 // 'gravity_vector_'.
 const Eigen::Quaterniond rotation = Eigen::Quaterniond::FromTwoVectors(
  gravity_vector_, orientation_.inverse() * Eigen::Vector3d::UnitZ());
 orientation_ = (orientation_ * rotation).normalized();
 //cout << "Orientation: " << orientation_ << endl;
 CHECK_GT((orientation_ * gravity_vector_).z(), 0.);

So I think my defaulting of this data is incorrect (As I don't have the sensors for the o/p)

An example of my data is:

header: 
  seq: 62350
  stamp: 
    secs: 1478974808
    nsecs: 401812741
  frame_id: imu_msg
orientation: 
  x: 0.573576460039
  y: 0.0
  z: -0.0
  w: -0.819152027703
orientation_covariance: [0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0]
angular_velocity: 
  x: 0.0
  y: 0.0
  z: 0.0
angular_velocity_covariance: [0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0]
linear_acceleration: 
  x: 0.0
  y: 0.0
  z: 0.0
linear_acceleration_covariance: [0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0]

Any help would me appreciated.

Thanks

Mark