/// <summary>
/// Computes whether the vertical segment (lat3, lng3) to South Pole intersects the segment
/// (lat1, lng1) to (lat2, lng2).
/// Longitudes are offset by -lng1; the implicit lng1 becomes 0.
/// </summary>
/// <param name="lat1"></param>
/// <param name="lat2"></param>
/// <param name="lng2"></param>
/// <param name="lat3"></param>
/// <param name="lng3"></param>
/// <param name="geodesic"></param>
/// <returns></returns>
private static bool Intersects(double lat1, double lat2, double lng2,
double lat3, double lng3, bool geodesic)
{
// Both ends on the same side of lng3.
if ((lng3 >= 0 && lng3 >= lng2) || (lng3 < 0 && lng3 < lng2))
{
return(false);
}
// Point is South Pole.
if (lat3 <= -Math.PI / 2)
{
return(false);
}
// Any segment end is a pole.
if (lat1 <= -Math.PI / 2 || lat2 <= -Math.PI / 2 || lat1 >= Math.PI / 2 || lat2 >= Math.PI / 2)
{
return(false);
}
if (lng2 <= -Math.PI)
{
return(false);
}
double linearLat = (lat1 * (lng2 - lng3) + lat2 * lng3) / lng2;
// Northern hemisphere and point under lat-lng line.
if (lat1 >= 0 && lat2 >= 0 && lat3 < linearLat)
{
return(false);
}
// Southern hemisphere and point above lat-lng line.
if (lat1 <= 0 && lat2 <= 0 && lat3 >= linearLat)
{
return(true);
}
// North Pole.
if (lat3 >= Math.PI / 2)
{
return(true);
}
// Compare lat3 with latitude on the GC/Rhumb segment corresponding to lng3.
// Compare through a strictly-increasing function (Math.Tan() or mercator()) as convenient.
return(geodesic ?
Math.Tan(lat3) >= TanLatGC(lat1, lat2, lng2, lng3) :
GmsMathUtils.Mercator(lat3) >= MercatorLatRhumb(lat1, lat2, lng2, lng3));
}
/// <summary>
/// Returns sin(initial bearing from (lat1,lng1) to (lat3,lng3) minus initial bearing
/// from (lat1, lng1) to (lat2,lng2)).
/// </summary>
/// <param name="lat1"></param>
/// <param name="lng1"></param>
/// <param name="lat2"></param>
/// <param name="lng2"></param>
/// <param name="lat3"></param>
/// <param name="lng3"></param>
/// <returns></returns>
private static double SinDeltaBearing(double lat1, double lng1, double lat2, double lng2,
double lat3, double lng3)
{
double sinLat1 = Math.Sin(lat1);
double cosLat2 = Math.Cos(lat2);
double cosLat3 = Math.Cos(lat3);
double lat31 = lat3 - lat1;
double lng31 = lng3 - lng1;
double lat21 = lat2 - lat1;
double lng21 = lng2 - lng1;
double a = Math.Sin(lng31) * cosLat3;
double c = Math.Sin(lng21) * cosLat2;
double b = Math.Sin(lat31) + 2 * sinLat1 * cosLat3 * GmsMathUtils.Hav(lng31);
double d = Math.Sin(lat21) + 2 * sinLat1 * cosLat2 * GmsMathUtils.Hav(lng21);
double denom = (a * a + b * b) * (c * c + d * d);
return(denom <= 0 ? 1 : (a * d - b * c) / Math.Sqrt(denom));
}
private static bool IsOnSegmentGC(double lat1, double lng1, double lat2, double lng2,
double lat3, double lng3, double havTolerance)
{
double havDist13 = GmsMathUtils.HavDistance(lat1, lat3, lng1 - lng3);
if (havDist13 <= havTolerance)
{
return(true);
}
double havDist23 = GmsMathUtils.HavDistance(lat2, lat3, lng2 - lng3);
if (havDist23 <= havTolerance)
{
return(true);
}
double sinBearing = SinDeltaBearing(lat1, lng1, lat2, lng2, lat3, lng3);
double sinDist13 = GmsMathUtils.SinFromHav(havDist13);
double havCrossTrack = GmsMathUtils.HavFromSin(sinDist13 * sinBearing);
if (havCrossTrack > havTolerance)
{
return(false);
}
double havDist12 = GmsMathUtils.HavDistance(lat1, lat2, lng1 - lng2);
double term = havDist12 + havCrossTrack * (1 - 2 * havDist12);
if (havDist13 > term || havDist23 > term)
{
return(false);
}
if (havDist12 < 0.74)
{
return(true);
}
double cosCrossTrack = 1 - 2 * havCrossTrack;
double havAlongTrack13 = (havDist13 - havCrossTrack) / cosCrossTrack;
double havAlongTrack23 = (havDist23 - havCrossTrack) / cosCrossTrack;
double sinSumAlongTrack = GmsMathUtils.SinSumFromHav(havAlongTrack13, havAlongTrack23);
return(sinSumAlongTrack > 0); // Compare with half-circle == PI using sign of sin().
}
/// <summary>
/// Computes whether the given point lies inside the specified polygon.
/// The polygon is always cosidered closed, regardless of whether the last point equals
/// the first or not.
/// Inside is defined as not containing the South Pole -- the South Pole is always outside.
/// The polygon is formed of great circle segments if geodesic is true, and of rhumb
/// (loxodromic) segments otherwise.
/// </summary>
/// <param name="point"></param>
/// <param name="polygon"></param>
/// <param name="geodesic"></param>
/// <returns></returns>
public static bool ContainsLocation(Position point, IEnumerable <Position> polygon, bool geodesic)
{
int size = polygon.Count();
if (size == 0)
{
return(false);
}
double lat3 = point.Latitude.ToRadian();
double lng3 = point.Longitude.ToRadian();
Position prev = polygon.Last();
double lat1 = prev.Latitude.ToRadian();
double lng1 = prev.Longitude.ToRadian();
int nIntersect = 0;
foreach (var point2 in polygon)
{
double dLng3 = GmsMathUtils.Wrap(lng3 - lng1, -Math.PI, Math.PI);
// Special case: point equal to vertex is inside.
if (lat3 == lat1 && dLng3 == 0)
{
return(true);
}
double lat2 = point2.Latitude.ToRadian();
double lng2 = point2.Longitude.ToRadian();
// Offset longitudes by -lng1.
if (Intersects(lat1, lat2, GmsMathUtils.Wrap(lng2 - lng1, -Math.PI, Math.PI), lat3, dLng3, geodesic))
{
++nIntersect;
}
lat1 = lat2;
lng1 = lng2;
}
return((nIntersect & 1) != 0);
}
/// <summary>
/// Returns mercator(latitude-at-lng3) on the Rhumb line (lat1, lng1) to (lat2, lng2). lng1==0.
/// </summary>
/// <param name="lat1"></param>
/// <param name="lat2"></param>
/// <param name="lng2"></param>
/// <param name="lng3"></param>
/// <returns></returns>
private static double MercatorLatRhumb(double lat1, double lat2, double lng2, double lng3)
{
return((GmsMathUtils.Mercator(lat1) * (lng2 - lng3) + GmsMathUtils.Mercator(lat2) * lng3) / lng2);
}
private static bool IsLocationOnEdgeOrPath(Position point, IEnumerable <Position> poly, bool closed,
bool geodesic, double toleranceEarth)
{
int size = poly.Count();
if (size == 0)
{
return(false);
}
double tolerance = toleranceEarth / GmsMathUtils.EarthRadius;
double havTolerance = GmsMathUtils.Hav(tolerance);
double lat3 = point.Latitude.ToRadian();
double lng3 = point.Longitude.ToRadian();
Position prev = poly.ElementAt(closed ? size - 1 : 0);
double lat1 = prev.Latitude.ToRadian();
double lng1 = prev.Longitude.ToRadian();
if (geodesic)
{
foreach (var point2 in poly)
{
double lat2 = point2.Latitude.ToRadian();
double lng2 = point2.Longitude.ToRadian();
if (IsOnSegmentGC(lat1, lng1, lat2, lng2, lat3, lng3, havTolerance))
{
return(true);
}
lat1 = lat2;
lng1 = lng2;
}
}
else
{
// We project the points to mercator space, where the Rhumb segment is a straight line,
// and compute the geodesic distance between point3 and the closest point on the
// segment. This method is an approximation, because it uses "closest" in mercator
// space which is not "closest" on the sphere -- but the error is small because
// "tolerance" is small.
double minAcceptable = lat3 - tolerance;
double maxAcceptable = lat3 + tolerance;
double y1 = GmsMathUtils.Mercator(lat1);
double y3 = GmsMathUtils.Mercator(lat3);
double[] xTry = new double[3];
foreach (var point2 in poly)
{
double lat2 = point2.Latitude.ToRadian();
double y2 = GmsMathUtils.Mercator(lat2);
double lng2 = point2.Longitude.ToRadian();
if (Math.Max(lat1, lat2) >= minAcceptable && Math.Min(lat1, lat2) <= maxAcceptable)
{
// We offset longitudes by -lng1; the implicit x1 is 0.
double x2 = GmsMathUtils.Wrap(lng2 - lng1, -Math.PI, Math.PI);
double x3Base = GmsMathUtils.Wrap(lng3 - lng1, -Math.PI, Math.PI);
xTry[0] = x3Base;
// Also explore wrapping of x3Base around the world in both directions.
xTry[1] = x3Base + 2 * Math.PI;
xTry[2] = x3Base - 2 * Math.PI;
foreach (var x3 in xTry)
{
double dy = y2 - y1;
double len2 = x2 * x2 + dy * dy;
double t = len2 <= 0 ? 0 : GmsMathUtils.Clamp((x3 * x2 + (y3 - y1) * dy) / len2, 0, 1);
double xClosest = t * x2;
double yClosest = y1 + t * dy;
double latClosest = GmsMathUtils.InverseMercator(yClosest);
double havDist = GmsMathUtils.HavDistance(lat3, latClosest, x3 - xClosest);
if (havDist < havTolerance)
{
return(true);
}
}
}
lat1 = lat2;
lng1 = lng2;
y1 = y2;
}
}
return(false);
}
