DescriptionInertialNav App Lite is primarily an attitude estimator/indicator, with the following instruments:
- artificial horizon.
- compass (magnetic)
- speed meter (groundspeed, vertical speed)
A HUD mode allows using the application for augmented reality.
Real-time measurements and estimations can be exported to a text file for post-processing (e.g. into MATLAB, SciLab or Octave).
HOW DOES IT WORK?
In real life environment, sensors tend to measure noises in addition to the physical quantity of interest. The current application provides an estimate of the attitude. To have the best estimation of the attitude an Extended Kalman Filter (EKF) is implemented. The filter's purpose is to reject all perturbations, but to do so efficiently, it needs different sources of measurments. Considering we are interested by the orientation, and your device is indeed an inertial measurement unit (IMU with gyroscopes, accelerometers and so on), using gyroscopes for angular velocity and a set of measurements from accelerometers and magnetometers, we can indeed estimate the attitude with our EKF. That is, to estimate the attitude, the EKF will sometimes discard information from the sensors that it deems unreliable or too noisy - it may sometimes favour the attitude measurements rather than the angular velocity integration and vice versa - to minimise the covariance of the error. Furthermore, quaternion formulation for the orientation makes the estimation very robust.
** IMPORTANT ** : depending on your device, please consider going through the covariance settings for best estimation of the attitude! The EKF may disregard the measurements if deemed unreliable. If YOU THINK the app does not use the gyroscopes, please CHECK the variance settings for the gyroscopes. The values to enter can be quite large. Try from 0.001 to 1e2 for instance.
How can you know whether the app uses gyroscopes or accerometers only?
- without gyroscopes, but with accelerometers, the attitude is very noisy (e.g., fast "jumps").
- without the accelerometers, but with the gyroscopes, the attitude is very smooth (because of the integration of gyro data), but there is a slow drift of the attitude increasing with time.
The full version of this app provides:
- ground track and estimation of the position (experimental).
- better estimation of the vertical speed.
- Google Map inclusion.
In the lite version, position data comes from GPS measurements only. Furthermore, the vertical speed is calculated from GPS measurements and can thus only be of limited accuracy.
For best performances, accelerometers, gyroscopes and magnetometers must all be present on the device.
Optional requirements: GPS, camera.
(HeadUp Display will only be available when a camera is available)
The application is provided as-is, without any warranty. The application is not certified for navigation purposes by any agency or organisation.
If you find bugs, please report by email. Thanks!
Tested on Samsung Galaxy S2.