Week 4 Summary

Pedestrian Tracking

Tracking a person is a challenging problem especially in outdoor environments that have to previous preparation. This capability would prove very useful for things like search and rescue, as well as tracking emergency response workers (like firefighters). The NavShoe is a concept attempting to address this problem by using a small motion sensor that fits in the laces and requires minimal battery.

Typically, using motion produces position errors that expand cubically in time. The NavShoe attempts to reduce this problem by taking measurements during stance to eliminate the error and reduce it to a linear problem (rather than a cubic one). There are a number of details about specific techniques used to resolve the heading drift problem in the sensor device.

In the implementation section, it describes how this process was achieved. I was slightly disappointed to hear that the GPS is accurate to 6 meters. This made me think that even though this technology is cool for accurate tracking – in most of the applications I can think of, a GPS is more than enough accuracy. There may, however, be some sort of medical applications requiring much more precision – but then again, a medical room is a controlled environment (indoors) and GPS can be replaced with much more accurate local positioning systems. There is quite a bit of rather boring Kalman Filter tracking math in this section that demonstrates the process used to implement the sensor. Interestingly – the iron in the shoe was assumed to mess with the registration, and so this was also accounted for in the filter. There is an exciting diagram showing the NavShoe’s path as registered by the system, and it is cool to see how accurate it seems to be.

The results of the outdoor experiment showed that the NavShoe seemed reasonably accurate within a few kilometers. With an available GPS, a lot of magnetic error can also be reduced, which further improves the system. Ultimately, the NavShoe excels in that a user can walk into a building, and out of GPS range, and for at least a few kilometers, the user can be accurate about continuing to track himself. This becomes a nice supplement to a MR system, which relies on accurate user tracking.

I wonder after having read this article – how reasonable is it to incorporate this device directly into a mobile phone?


Week 4 Summary

Pedestrian Tracking with Shoe-Mounted Inertial Sensors

The paper describes the NavShoe system suitable for position tracking based on inertial sensing. Real world deployment of location sensors then required an instrumented or marked environment. The Navshoe system overcomes this problem by enabling position tracking without preparing any indoor or outdoor setting. It basically uses a miniature inertial/magnetometer package wirelessly coupled to a PDA. Its key feature is that it works in environments both with and without GPS support, it is low power and low cost.  Additionally the device is so small (1 inch * 1 inch) that it can be easily slipped under users shoelaces. It is quite accurate with a 6 meter root mean square accuracy. It actually overcomes the cubic in time error growth  by detecting only the stance phase and applying zero velocity updates as psuedomeasurements into the Extended Kalman Filter error corrector. This results in linear error accumulation with the number of steps. This makes the NavShoe system accurate enough for moderate distances and for longer distances it can be used in conjunction with GPS to provide a hybrid GPS/inertial solution which is more accurate. It is thus suitable for rescuing firefighters, navigation assistance,mobile 3d audio and other mixed or AR applications.

Among several others one question that I would like to discuss is that other than indoor emergency situations is such accurate position tracking actually required? Isnt the GPS technology advance enough to meet most of our needs.

Week 4 Summary

Pedestrian Tracking with Shoe-Mounted Inertial Sensors
The paper describes NavShoe, a pedestrian navigation system which tracks the location of a person on foot. NavShoe provides real-time location data of individuals in GPS denied areas without the need of pre-existing infrastructure. The system makes use of an wireless inertial sensor which is small enough to fit into shoe laces and run on low power. NavShoe can be used to determine real-time tracking of soldiers, workers in hazardous environment, people engaged in rescue operations for ex. firefighters etc.
 The highlight of the system is that it can be coupled with a RF or GPS in order to provide accurate thee-dimensional position and location co-ordinates. It is independent of the stride length and pace at which the person walks. The indoor and outdoor experiments both showed high accuracy. Even though the NavShoe system is fairly small it is highly sophisticated since it contains both hardware and software components to it.
Hardware consists of a nine-element multisensor containing gyros, accelerometers, and magnetometers. The radio supports 16 RF channels, The software is responsible to track initial position and correct heading direction with a magnetic compass.
The fact that now it is wireless and does not require any calibration makes the functionality even more commendable. I would like to ask the author is whether the tests were conducted in any kind of a controlled environment to test the accuracy of the system. Cause if they were not then I feel that the NavShoe and similar technology systems might be ready to be used in a wide field of applications like Military, Surveillance, BioMechanics even Sports to a great extent.

week 4 summary – Hitesh

The paper highlights some of the existing issues with location based tracking systems in a real world MR and wearable systems, that it requires the objects in the environment to be pre-mapped or marked thus not making the system extensible and robust. Computer vision tracking poses a lot of challenges and requires complex algorithms and corrections to be implemented. InterSense proposes to solve this issue through inertial sensors. The inertial cubes in the foot provide more accurate tracking than head-mounted orientation tracking because it enables Transfer Alignment based on acceleration/deceleration along an axis relative to the rest position.

The Navshoe improves accuracy by applying zero velocity update (ZUPT) to EKF when it detects a stance phase after each stride to correct the drift velocity error. The Navshoe provides considerable accuracy over short distances and has the ability to track height example each stair on a staircase. GPS can be used to extend range and correct yaw drift error. The information is also not affected by magnetic disturbances.  The system can be used in conjunction with MR and head tracking systems to improve yaw accuracy by providing reference points.