// calculates the distance from start to the point projected onto the line
private double getDistanceAlongLine(GpxPoint point)
{
double distanceA = 1000 * GpxParser.gpsToGpx(startingPoint).GetDistanceFrom(point); // distances to start point
double cos_phi = getCosPhi(point);
return(cos_phi * distanceA);
}
// calculates cos(phi) where phi is the angle between the line and a line from the start point to the current point
private double getCosPhi(GpxPoint point)
{
// distances to start/end point
double distanceA = 1000 * GpxParser.gpsToGpx(startingPoint).GetDistanceFrom(point);
double distanceB = 1000 * GpxParser.gpsToGpx(endPoint).GetDistanceFrom(point);
// using cosine theorem; phi is the angle between the line and a line from the start point to the current point
double cos_phi = (lineLength * lineLength + distanceA * distanceA - distanceB * distanceB) / (2 * lineLength * distanceA);
if (cos_phi > 1) // prevents errors due to rounding
{
return(1);
}
else if (cos_phi < -1)
{
return(-1);
}
else
{
return(cos_phi);
}
}
public CalculationResult calculate()
{
CalculationResult result;
lineLength = 1000 * GpxParser.gpsToGpx(startingPoint).GetDistanceFrom(GpxParser.gpsToGpx(endPoint)); // length of the line
// calculate deviations
List <double> deviations = new List <double>();
List <double> distancesAlongLine = new List <double>();
foreach (GpxPoint point in gpxData)
{
deviations.Add(getDeviation(point));
distancesAlongLine.Add(getDistanceAlongLine(point));
}
// calculate metrics
result.deviations = deviations;
result.awgDeviation = getAwgDeviation(deviations);
result.awgSquareDeviation = getAwgSquareDeviation(deviations);
result.area = getArea(deviations, distancesAlongLine);
result.areaNorm = result.area / lineLength;
result.over10 = percentageOverThreshold(deviations, 10);
result.over25 = percentageOverThreshold(deviations, 25);
result.over50 = percentageOverThreshold(deviations, 50);
result.over80 = percentageOverThreshold(deviations, 80);
result.over120 = percentageOverThreshold(deviations, 120);
result.numOver10 = numberOverThreshold(deviations, 10);
result.numOver25 = numberOverThreshold(deviations, 25);
result.numOver50 = numberOverThreshold(deviations, 50);
result.numOver80 = numberOverThreshold(deviations, 80);
result.numOver120 = numberOverThreshold(deviations, 120);
result.maxDeviation = getMaximumDeviation(deviations);
// create histogram data
result.histogramData = getHistogramData(deviations);
return(result);
}
// calculates the deviation of a point to the line
private double getDeviation(GpxPoint point)
{
double distanceA = 1000 * GpxParser.gpsToGpx(startingPoint).GetDistanceFrom(point); // distances to start point
double cos_phi = getCosPhi(point);
double sin_phi = System.Math.Sqrt(1 - cos_phi * cos_phi);
// deviation is the heigth of the triangle
double deviation = sin_phi * distanceA;
// if point is left of the line, deviation is negativ
double deltaLong = endPoint.Longitude - startingPoint.Longitude;
double deltaLat = endPoint.Latitude - startingPoint.Latitude;
double slope = deltaLat / deltaLong;
if (slope * (point.Longitude - startingPoint.Longitude) < point.Latitude - startingPoint.Latitude)
{
deviation *= -1;
}
if (startingPoint.Longitude > endPoint.Longitude) // the direction you walk the line changes left/right
{
deviation *= -1;
}
return(deviation);
}