I wish to get the distance to a line and started using haversine code.
private static final double _eQuatorialEarthRadius = 6378.1370D;
private static final double _d2r = (Math.PI / 180D);
private static double PRECISION = 0.001;
// Haversine Algorithm
// source: http://stackoverflow.com/questions/365826/calculate-distance-between-2-gps-coordinates
private static double HaversineInM(double lat1, double long1, double lat2, double long2) {
return (1000D * HaversineInKM(lat1, long1, lat2, long2));
}
private static double HaversineInKM(double lat1, double long1, double lat2, double long2) {
double dlong = (long2 - long1) * _d2r;
double dlat = (lat2 - lat1) * _d2r;
double a = Math.pow(Math.sin(dlat / 2D), 2D) + Math.cos(lat1 * _d2r) * Math.cos(lat2 * _d2r)
* Math.pow(Math.sin(dlong / 2D), 2D);
double c = 2D * Math.atan2(Math.sqrt(a), Math.sqrt(1D - a));
double d = _eQuatorialEarthRadius * c;
return d;
}
// Distance between a point and a line
public static double pointLineDistanceTest(double[] aalatlng,double[] bblatlng,double[] ttlatlng) {
double [] a = aalatlng;
double [] b = bblatlng;
double [] c = ttlatlng;
double[] nearestNode = nearestPointGreatCircle(a, b, c);
// System.out.println("nearest node: " + Double.toString(nearestNode[0]) + "," + Double.toString(nearestNode[1]));
double result = HaversineInM(c[0], c[1], nearestNode[0], nearestNode[1]);
// System.out.println("result: " + Double.toString(result));
return (result);
}
// source: http://stackoverflow.com/questions/1299567/how-to-calculate-distance-from-a-point-to-a-line-segment-on-a-sphere
private static double[] nearestPointGreatCircle(double[] a, double[] b, double c[])
{
double[] a_ = toCartsian(a);
double[] b_ = toCartsian(b);
double[] c_ = toCartsian(c);
double[] G = vectorProduct(a_, b_);
double[] F = vectorProduct(c_, G);
double[] t = vectorProduct(G, F);
return fromCartsian(multiplyByScalar(normalize(t), _eQuatorialEarthRadius));
}
@SuppressWarnings("unused")
private static double[] nearestPointSegment (double[] a, double[] b, double[] c)
{
double[] t= nearestPointGreatCircle(a,b,c);
if (onSegment(a,b,t))
return t;
return (HaversineInKM(a[0], a[1], c[0], c[1]) < HaversineInKM(b[0], b[1], c[0], c[1])) ? a : b;
}
private static boolean onSegment (double[] a, double[] b, double[] t)
{
// should be return distance(a,t)+distance(b,t)==distance(a,b),
// but due to rounding errors, we use:
return Math.abs(HaversineInKM(a[0], a[1], b[0], b[1])-HaversineInKM(a[0], a[1], t[0], t[1])-HaversineInKM(b[0], b[1], t[0], t[1])) < PRECISION;
}
// source: http://stackoverflow.com/questions/1185408/converting-from-longitude-latitude-to-cartesian-coordinates
private static double[] toCartsian(double[] coord) {
double[] result = new double[3];
result[0] = _eQuatorialEarthRadius * Math.cos(Math.toRadians(coord[0])) * Math.cos(Math.toRadians(coord[1]));
result[1] = _eQuatorialEarthRadius * Math.cos(Math.toRadians(coord[0])) * Math.sin(Math.toRadians(coord[1]));
result[2] = _eQuatorialEarthRadius * Math.sin(Math.toRadians(coord[0]));
return result;
}
private static double[] fromCartsian(double[] coord){
double[] result = new double[2];
result[0] = Math.toDegrees(Math.asin(coord[2] / _eQuatorialEarthRadius));
result[1] = Math.toDegrees(Math.atan2(coord[1], coord[0]));
return result;
}
// Basic functions
private static double[] vectorProduct (double[] a, double[] b){
double[] result = new double[3];
result[0] = a[1] * b[2] - a[2] * b[1];
result[1] = a[2] * b[0] - a[0] * b[2];
result[2] = a[0] * b[1] - a[1] * b[0];
return result;
}
private static double[] normalize(double[] t) {
double length = Math.sqrt((t[0] * t[0]) + (t[1] * t[1]) + (t[2] * t[2]));
double[] result = new double[3];
result[0] = t[0]/length;
result[1] = t[1]/length;
result[2] = t[2]/length;
return result;
}
private static double[] multiplyByScalar(double[] normalize, double k) {
double[] result = new double[3];
result[0] = normalize[0]*k;
result[1] = normalize[1]*k;
result[2] = normalize[2]*k;
return result;
}
and had many errors so wrote this to calculate using bearings to get the angle then using distance (point a, target) to calculate the target to (point a, point b) line. Point A and B are the line and I want the distance from target to line. No great circle. sin angle (difference in bearings) *point a to target distance= Length of the side of a right angle triangle from the right angle on AB line to target.
public double pointlinedistancetest(){
//set latlng location point a
Location apoint=new Location("");
apoint.setLatitude(lata);
apoint.setLongitude(lona);
//set latlng location point b
Location bpoint=new Location("");
bpoint.setLatitude(latb);
bpoint.setLongitude(lonb);
//set latlng location target to get dis to line
Location tpoint=new Location("");
tpoint.setLatitude(lat);
tpoint.setLongitude(lon);
float pbearingf = apoint.bearingTo(bpoint);
float tbearingf= apoint.bearingTo(tpoint);
double tb=tbearingf;
double ab=pbearingf;
//get angle degree difference
float angle= Math.min((pbearingf-tbearingf)<0?pbearingf-tbearingf+360:pbearingf-tbearingf, (tbearingf-pbearingf)<0?tbearingf-pbearingf+360:tbearingf-pbearingf);
// float angle= Math.min((tbearingf-pbearingf)<0?tbearingf-pbearingf+360:tbearingf-pbearingf, (pbearingf-tbearingf)<0?pbearingf-tbearingf+360:pbearingf-tbearingf);
// min((a1-a2)<0?a1-a2+360:a1-a2, (a2-a1)<0?a2-a1+360:a2-a1)
double aabearing=angle;
float atot=apoint.distanceTo(tpoint);
double atotdis=atot;
//right angle triangle formula
dis=(Math.sin(aabearing))*atotdis;
return (dis);
}
Now both are still showing massive errors of up to 30%. Does this code look correct and is there any better way of doing this or are my errors else where. My GPS is showing 4 metre accuracy and my formulas(code) is showing errors of 10 to 20 metres and does not seem to be remotely the same.
