QML PositionSource supporting map matching
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PositionSourceMapMatched.qml
README.md

README.md

QML PositionSource with map matching support

This is a QML type - PositionSourceMapMatched - that is designed to be an extended PositionSource. In addition to regular PositionSource functionality, it allows to determine current street name, direction of travel along the street, current speed limit. For that, it communicates with local OSM Scout Server and uses map maptching functionality of Valhalla.

Communication between PositionSourceMapMatched and OSM Scout Server is implemented through DBus. Thus, to use this QML type, you would need

The maps required for map matching can be downloaded by OSM Scout Server (GUI recommended).

While, at present, the type exposes only street name, direction, and speed limit, it can be easily extended to provide other information supported by Valhalla's map matching functionality. Note that it is focused on just-in-time data, not longer stretches.

Usage

The code is contained in a single QML file. So, copy PositionSourceMapMatched.qml into your source tree and use it via local import. Since its licensed under MIT license, it should be compatible with the variuos open source and proprietary licenses.

When used in the program, if the map matching mode is enabled, PositionSourceMapMatched will automatically request map matched position and available data regarding it. If needed, it will try to start OSM Scout Server through systemd socket activation and will follow apperance / disappearance of the server on D-Bus. The corresponding status is communicated via properties.

In addition to regular usage, there are facilities for the use of the type in testing environment (feeding coordinates from outside) and timing statistics.

See included example for usage of PositionSourceMapMatched and showing available data.

API

The exported API follows QML PositionSource.

The main limitations, when compared to the PositionSource, are:

  • position property is replaced by JS Object with the same properties as the original. Thus, there are no methods or signals associated with the changes with the properties of position (for example, you cannot follow onAltitudeValidChanged signal of position). However, changes in position property are signaled, as usual, via on onPositionChanged of PositionSourceMapMatched.

  • signal updateTimeout() is not propagated due to the absence of this signal in Sailfish QtPositioning module. Feel free to uncomment the corresponding code in master and gps sections of the code.

The public API is extending PositionSource via additional properties. Below, the properties are described by their use: production, testing, and timining.

Properties

  • real direction Direction of travel along the matched street or path. Given in degrees from true north.

  • bool directionValid True if direction contains valid data

  • bool mapMatchingAvailable True if OSM Scout Server is running and exposing map matching via D-Bus

  • int mapMatchingMode Requested map matching mode. This follows enum Mode values in valhallamapmatcher.h of OSM Scout Server code. At present, the following modes are available (value and its meaning listed below):

    • 0 no map matching
    • 1 car, "auto" in Valhalla API
    • 2 car along shorter distance, "auto_shorter" in Valhalla API
    • 3 bicycle
    • 4 bus
    • 5 pedestrian

    Care will be taken to keep map matching modes backwards compatible and only extension of the values is planned, if needed.

  • string streetName Street name of the matched Valhalla's edge. Can be empty due to the failed map matching or in the absence of the street name in OSM data.

  • real streetSpeedAssumed Speed assumed for traveling along the matched Valhalla's edge. Speed is given in meters/second, negative in the absence of data.

  • real streetSpeedLimit Speed limit for traveling along the matched Valhalla's edge. Speed is given in meters/second, negative in the absence of data.

Timing statistics properties

Timing statistics allows to determine performance of map matching. Statistics is given by average, minimum and maximum call times. Call time is defined as a time elapsed from obtaining GPS position change till receiving and processing the response of map matching algorithm.

  • bool timingStatsEnable Set to true to enable timing statistics. Statistics will be collected from the moment this property is set to true.

  • real timingOverallAvr Average call time for map matching in seconds.

  • real timingOverallMax Maximal call time for map matching in seconds.

  • real timingOverallMin Minimal call time for map matching in seconds.

Testing

To simplify debugging in the absence of GPS signal, one can provide coordinates by using testingCoordinate property. For example, as has been done earlier for Poor Maps by @otsaloma, one can hook changes in map center QML item to this property. As soon as testingCoordinate is set, a timer will be started that will update internal PositionSourceMapMatched with the same period as requested by updateInterval. To stop such testing, set testingCoordinate to undefined.

See included example for how to use this feature.