Pedestrian Dead Reckoning Crab Angle Sensor Orientation
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Solution Overview
Problem
Pedestrian navigation indoors is challenging due to the limitations of GPS and WiFi, as they consume power quickly and are not available indoors, and existing pedestrian dead-reckoning methods struggle to accurately determine the heading direction of a portable device relative to user movement.
Innovation Solution
A system and method using accelerometer data to calculate the 'crab angle' and combine it with magnetometer and gyroscope data to improve pedestrian dead-reckoning, compensating for device orientation changes and gait disturbances through synchronous averaging and Kalman filtering, allowing for accurate determination of user heading and position indoors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If GNSS is used for localization, then positioning accuracy is improved, but power consumption increases and it becomes unavailable indoors
Solution Approach 1:
The system uses the mobile device's own sensors (accelerometer, magnetometer, gyroscope) to determine position and orientation, eliminating dependence on external infrastructure like GNSS or WiFi. The accelerometer detects gait patterns and the magnetometer provides heading information, allowing the device to self-determine its location through dead reckoning from a known starting point.
2Ease of operation
If device orientation is used to determine user heading, then navigation information is available, but accuracy deteriorates due to device swinging and unpredictable orientation changes
Solution Approach 1:
The system extracts the stable magnetic field direction from the magnetometer data to determine heading, separating this reliable directional information from the noisy device orientation data. By using the magnetometer's magnetic north reference rather than relying on device orientation sensors, the system extracts a stable heading signal that is not affected by device swinging or unpredictable orientation changes.
Solution Approach 2:
The magnetometer acts as an intermediary to provide a stable magnetic north reference that mediates between the device's physical orientation and the user's actual movement direction. This magnetic reference frame serves as a stable intermediary that allows the system to determine heading independent of how the device is being held or moved by the user.
3Productivity
If accelerometer data is used for step detection, then movement information is obtained, but signal stability deteriorates due to gait disturbances and device motion
Solution Approach 1:
The system performs preliminary processing of accelerometer data by detecting gait patterns and identifying step events before using this information for position calculation. By detecting the periodic nature of gait and synchronizing measurements with step events, the system prepares the data in advance to filter out gait-related disturbances and isolate the useful motion information.
Data Source
AI summary
A method and system are provided for improved pedestrian dead reckoning. In an embodiment, the crab angle of a device, i.e., the angle by which the device direction of travel differs from the device orientation, is determined via the processing of measurements from a vector accelerometer. The measured acceleration vector is rotated so that one component is vertical, and the crab angle is then found by determining a horizontal direction having the greatest energy. Correlations between the two horizontal acceleration components and the vertical acceleration component may be computed to determine the user's gait, further improving dead reckoning, e.g., for improving indoor position resolution.