The HERE iOS SDK performs Map Matching automatically when it needs to match a raw position to the road network, such as during drive guidance, where there may be inaccuracies in the road rendering or GPS data. Map matching also supports instances where the GPS signal is lost while entering a road tunnel. The position is extrapolated and updated based on the driver’s speed and knowledge of the tunnel layout.
Automotive Map Matching
The HERE iOS SDK supports high-accuracy map matching through the
NMAPositionDataSourceAutomotive class. As a requirement to use this class, you must have positioning data input from a GNSS module that supports dead reckoning. This ensures a continuous and reliable stream of position updates even in cases where the GPS becomes unavailable (for example, when the user is driving in a tunnel). It is strongly recommended that position updates are provided, at a constant rate of 10 Hz, together with standard deviations of the following:
- Horizontal radial error (large component)
- Horizontal radial error (small component)
- Automotive Map Matching is currently offered as a beta feature. APIs may change without notice.
- Automotive Map Matching does not support tunnel extrapolation.
Custom Data Sources
In general, you can also use any custom positioning data by implementing the
NMAPositionDataSource class and set it to the
dataSource property in
NMAPositioningManager before starting the positioning manager.