public ListeningSpeedProbe()
{
_positionChangedHandler = async(o, e) =>
{
if (e.Position == null)
{
return;
}
Datum datum = null;
lock (_locker)
{
SensusServiceHelper.Get().Logger.Log("Received position change notification.", LoggingLevel.Verbose, GetType());
if (_previousPosition == null)
{
_previousPosition = e.Position;
}
else if (e.Position.Timestamp > _previousPosition.Timestamp) // it has happened (rarely) that positions come in out of order...drop any such positions.
{
datum = new SpeedDatum(e.Position.Timestamp, _previousPosition, e.Position);
_previousPosition = e.Position;
}
}
if (datum != null)
{
await StoreDatumAsync(datum);
}
};
}
public SpeedDatum(DateTimeOffset timestamp, Position previousPosition, Position currentPosition)
: base(timestamp, 0)
{
double distanceKM;
double timeHours;
_kph = SpeedDatum.CalculateSpeedKPH(previousPosition, currentPosition, out distanceKM, out timeHours);
if (previousPosition.Accuracy >= 0 && currentPosition.Accuracy >= 0)
{
double maximumDistanceKM = distanceKM + previousPosition.Accuracy / 1000f + currentPosition.Accuracy / 1000f;
double maximumSpeedKPH = maximumDistanceKM / timeHours;
Accuracy = (float)(maximumSpeedKPH - _kph);
}
}
protected override IEnumerable <Datum> Poll(CancellationToken cancellationToken)
{
SpeedDatum datum = null;
Position currentPosition = GpsReceiver.Get().GetReading(cancellationToken);
if (currentPosition == null)
{
throw new Exception("Failed to get GPS reading.");
}
else
{
lock (_previousPositionLocker)
{
if (_previousPosition == null)
{
_previousPosition = currentPosition;
}
else if (currentPosition.Timestamp > _previousPosition.Timestamp) // it has happened (rarely) that positions come in out of order...drop any such positions.
{
datum = new SpeedDatum(currentPosition.Timestamp, _previousPosition, currentPosition);
_previousPosition = currentPosition;
}
}
}
if (datum == null)
{
return new Datum[] { }
}
; // datum will be null on the first poll and where polls return locations out of order (rare). these should count toward participation.
else
{
return new Datum[] { datum }
};
}