/// <summary> /// Creates coordinate in between two trace points to smooth line /// </summary> /// <returns>double array containing lng/lat</returns> private double[] pointAtDistanceAndBearing(TracePoint tracePoint, double distance, double bearing) { return(_ruler.Destination( new double[] { tracePoint.Longitude, tracePoint.Latitude } , distance , bearing )); }
/// <summary> /// Extract probes according to ProbeExtractorOptions. /// </summary> /// <param name="trace">List of trace points</param> /// <returns>List of probes. Empty list if no trace point matched the options.</returns> public List <Probe> ExtractProbes(List <TracePoint> trace) { int tracePntCnt = trace.Count; long[] durations = new long[tracePntCnt - 1]; double[] distances = new double[tracePntCnt - 1]; double[] speeds = new double[tracePntCnt - 1]; double[] bearings = new double[tracePntCnt - 1]; for (int i = 1; i < tracePntCnt; i++) { TracePoint current = trace[i]; TracePoint previous = trace[i - 1]; int insertIdx = i - 1; durations[insertIdx] = (current.Timestamp - previous.Timestamp) / 1000; //seconds double[] currLocation = new double[] { current.Longitude, current.Latitude }; double[] prevLocation = new double[] { previous.Longitude, previous.Latitude }; distances[insertIdx] = _ruler.Distance(currLocation, prevLocation); speeds[insertIdx] = distances[insertIdx] / durations[insertIdx] * 3600; //kph double bearing = _ruler.Bearing(prevLocation, currLocation); bearings[insertIdx] = bearing < 0 ? 360 + bearing : bearing; } List <Probe> probes = new List <Probe>(); // 1st pass: iterate trace points and determine if they are good // bail early if !_options.OutputBadProbes bool negativeDuration = false; for (int i = 1; i < speeds.Length; i++) { //assume tracpoint is good bool isGood = true; if (negativeDuration) { // if trace already has a negative duration, then all probes are bad isGood = false; } else if (durations[i] < 0) { // if a trace has negative duration, the trace is likely noisy // bail, if we don't want bad probes if (!_options.OutputBadProbes) { return(new List <Probe>()); } negativeDuration = true; isGood = false; } else if (durations[i] < _options.MinTimeBetweenProbes) { // if shorter than the minTimeBetweenProbes, filter. isGood = false; } else if (durations[i] > _options.MaxDurationRatioJump * durations[i - 1]) { // if not a gradual decrease in sampling frequency, it's most likely a signal jump isGood = false; } else if (speeds[i] - speeds[i - 1] > _options.MaxAcceleration * durations[i]) { // if accelerating faster than maxAcceleration, it's most likely a glitch isGood = false; } else if (speeds[i - 1] - speeds[i] > _options.MaxDeceleration * durations[i]) { // if decelerating faster than maxDeceleration, it's most likely a glitch isGood = false; } else { bool isForwardDirection = compareBearing(bearings[i - 1], bearings[i], 89, false); if (!isForwardDirection) { isGood = false; } } if (isGood || _options.OutputBadProbes) { double[] coords = pointAtDistanceAndBearing( trace[i - 1] , distances[i] / 2 , bearings[i] ); probes.Add(new Probe() { Latitude = coords[1], Longitude = coords[0], StartTime = trace[i].Timestamp, Duration = durations[i], Distance = distances[i], Speed = speeds[i], Bearing = bearings[i], IsGood = isGood }); } } // if too few good probes, drop entire trace if (!_options.OutputBadProbes && probes.Count < _options.MinProbes) { return(new List <Probe>()); } // MinProbes can be 0, return if (probes.Count == 0 && _options.MinProbes == 0) { return(new List <Probe>()); } // 2nd pass // require at least two probes if (probes.Count > 1) { // check first probe in a trace against the average of first two good probes var avgSpeed = (probes[0].Speed + probes[1].Speed) / 2; var avgDistance = (probes[0].Distance + probes[1].Distance) / 2; var avgDuration = (probes[0].Duration + probes[1].Duration) / 2; var avgBearing = averageAngle(probes[0].Bearing, probes[1].Bearing); bool good = true; if (negativeDuration) { if (!_options.OutputBadProbes) { return(new List <Probe>()); } negativeDuration = true; good = false; // if a trace has negative duration, the trace is likely noisy } else if (durations[0] < 0) { good = false; } else if (durations[0] < _options.MinTimeBetweenProbes) { // if shorter than the minTimeBetweenProbes, filter. good = false; } else if (distances[0] > _options.MaxDistanceRatioJump * avgDistance) { // if not a gradual increase in distance, it's most likely a signal jump good = false; } else if (durations[0] > _options.MaxDurationRatioJump * avgDuration) { // if not a gradual decrease in sampling frequency, it's most likely a signal jump good = false; } else if (avgSpeed - speeds[0] > _options.MaxAcceleration * durations[0]) { // if accelerating faster than maxAcceleration, it's most likely a glitch good = false; } else if (speeds[0] - avgSpeed > _options.MaxDeceleration * durations[0]) { // if decelerating faster than maxDeceleration, it's most likely a glitch good = false; } else { // if in reverse direction, it's most likely signal jump bool isForwardDirection = compareBearing(bearings[0], avgBearing, 89, false); if (!isForwardDirection) { good = false; } } if (good || _options.OutputBadProbes) { double[] coords = pointAtDistanceAndBearing( trace[0] , distances[0] , bearings[0] ); probes.Insert( 0, new Probe() { Latitude = coords[1], Longitude = coords[0], StartTime = trace[0].Timestamp, Duration = durations[0], Distance = distances[0], Speed = speeds[0], Bearing = bearings[0], IsGood = good } ); } } return(probes); }