Navigation Device Adaptive Threshold Map Matching
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Solution Overview
Problem
Existing navigation technologies face challenges in accurately calculating a current location using map matching due to varying measurement characteristics of GPS receivers and sensors across different mobile devices, leading to difficulties in selecting appropriate candidate points and determining if the current location is on or off a road.
Innovation Solution
A navigation device with a referenced-point setting unit and an out-of-road determination unit that calculates an evaluation target correlation value to determine the likelihood of the current location being on a road, using a statistical approach to set a threshold value based on historical data and distribution models, regardless of the measurement device used.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a predetermined threshold value is used to select candidate points from among those within a certain distance from the base location, then the selection process is simple and fast, but the accuracy of current location calculation deteriorates because candidate points may be excluded that should be included due to device-specific measurement variations
Solution Approach 1:
The patent applies dynamics by making the threshold value adaptive rather than fixed. The determination unit dynamically adjusts the threshold value based on the measurement device type (GPS receiver, sensor, or their combination) and current measurement characteristics. This allows the system to maintain both computational efficiency and measurement accuracy across different mobile devices by adjusting the threshold according to actual device performance rather than using a universal predetermined value
Solution Approach 2:
The patent implements parameter changes by modifying the threshold value parameter based on device-specific characteristics. The system changes the threshold parameter according to the type of measurement device being used (GPS-only, sensor-only, or combined systems) and adjusts it based on observed measurement errors and correlation values. This parameter adaptation resolves the contradiction by allowing the threshold to be both computationally simple to determine and accurately reflective of device-specific measurement capabilities
2Device complexity
If a fixed threshold value is used for map matching, then the processing is straightforward and efficient, but the reliability deteriorates because the threshold cannot adapt to different measurement devices and measurement environments
Solution Approach 1:
The patent applies self-service by enabling the system to automatically determine appropriate threshold values based on its own measurement characteristics. The determination unit monitors measurement errors and correlation values from the navigation device's own sensors and GPS receiver, and uses this self-observed data to adaptively set the threshold. This self-adjusting mechanism maintains processing simplicity while significantly improving reliability across different devices and environments
Solution Approach 2:
The patent implements feedback by creating a closed-loop system where the determination unit continuously monitors measurement correlation values and adjusts the threshold accordingly. The system uses feedback from measurement errors and the correlation between measured and map-based locations to refine the threshold value. This feedback mechanism ensures that the threshold adapts to changing measurement conditions while maintaining both process simplicity and calculation reliability
Data Source
AI summary
A current location measured by a GPS receiver is defined as a base location. Individual points fairly near to the base location that are located on roads whose distances from the base location fall within a predetermined distance are set as candidate points. A distance between the base location and a candidate point to be evaluated is calculated. In a case where the distance is larger than a threshold value statistically estimated from a history of calculated distances between the base location and previously set candidate points that draw a trajectory on a road leading to the candidate point to be evaluated, the threshold value defining a rough upper limit of a distribution range of distances between the base location and the candidate points, it is judged that a true current location is not located on the road in which the candidate point is located.