/// <summary>
/// Creates basic filter expression for location. This filter is not precise filter,
/// it will just filter out the majority of the identities that the caller is not interested it.
/// </summary>
/// <param name="LocationFilter">GPS location of the target area centre.</param>
/// <param name="Radius">Target area radius in metres.</param>
/// <returns>Filter expression for the database query.</returns>
public static Expression <Func <Q, bool> > GetLocationFilterExpression <Q>(GpsLocation LocationFilter, uint Radius) where Q : IdentityBase
{
log.Trace("(LocationFilter:'{0:US}',Radius:{1})", LocationFilter, Radius);
Expression <Func <Q, bool> > res = null;
// There are several separated cases:
// 1) Radius is very large - i.e. greater than 5,000 km. In this case, we do no filtering on this level at all.
// 2) Distance of the target area centre to one of the poles is not larger than the radius. In this case, we calculate latitude and longitude ranges,
// from which we then construct a target rectangle on the sphere that will represent our target area of interest.
// 3) Distance of the target area centre to one of the poles is larger than the radius. In this case, we only set some of the boundaries,
// but we will not have a full rectangle on the sphere. There are several subcases here described below.
// 1) Radius is very large, no filtering.
if (Radius > 5000000)
{
log.Trace("(-)[LARGE_RADIUS]");
return(res);
}
GpsLocation northPole = new GpsLocation(90.0m, 0.0m);
GpsLocation southPole = new GpsLocation(-90.0m, 0.0m);
double northPoleDistance = LocationFilter.DistanceTo(northPole);
double southPoleDistance = LocationFilter.DistanceTo(southPole);
double radius = (double)Radius;
if (radius >= northPoleDistance)
{
// 2) Distance to pole is not larger than the radius:
// a) North Pole
//
// In this case we go to the South from the centre to find the minimal latitude
// and there will be no limit on longitude.
GpsLocation minLatitudeLocation = LocationFilter.GoVector(GpsLocation.BearingSouth, radius);
log.Trace("Radius >= North Pole Distance, min latitude is {0}.", minLatitudeLocation.Latitude);
res = i => i.InitialLocationLatitude >= minLatitudeLocation.Latitude;
}
else if (radius >= southPoleDistance)
{
// 2) Distance to pole is not larger than the radius:
// b) South Pole
//
// In this case we go to the North from the centre to find the maximal latitude.
// and there will be no limit on longitude.
GpsLocation maxLatitudeLocation = LocationFilter.GoVector(GpsLocation.BearingNorth, radius);
log.Trace("Radius >= South Pole Distance, max latitude is {0}.", maxLatitudeLocation.Latitude);
res = i => i.InitialLocationLatitude <= maxLatitudeLocation.Latitude;
}
else
{
// 3) Distance to poles is larger than the radius.
//
// In this case we create a rectangle on the sphere, in which the target identities are expected to be.
// Using this square we will find latitude and longitude ranges for the database query.
// Find a GPS square that contains the whole target circle area.
GpsSquare square = LocationFilter.GetSquare((double)Radius);
// Get latitude range - this is simple, left-top and right-top corners define the max latitude,
// and left-bottom and right-bottom corners define the min latitude.
decimal maxLatitude = square.MidTop.Latitude;
decimal minLatitude = square.MidBottom.Latitude;
log.Trace("GPS square is {0:US}, min latitude is {1}, max latitude is {2}.", square, minLatitude, maxLatitude);
// Get longitude range - we have to examine all four corners here as it depends on which hemisphere they are
// and there are several different cases due to possibility of crossing longitude 180.
bool leftCornersSameSign = Math.Sign(square.LeftBottom.Longitude) == Math.Sign(square.LeftTop.Longitude);
bool rightCornersSameSign = Math.Sign(square.RightBottom.Longitude) == Math.Sign(square.RightTop.Longitude);
if (leftCornersSameSign && rightCornersSameSign && (Math.Sign(square.LeftTop.Longitude) == Math.Sign(square.RightTop.Longitude)))
{
// a) Square does not cross longitude 180. This case is simple, we find left most and right most longitudes
// and our target profiles has to be between those two.
decimal leftLongitude = Math.Min(square.LeftTop.Longitude, square.LeftBottom.Longitude);
decimal rightLongitude = Math.Max(square.RightTop.Longitude, square.RightBottom.Longitude);
log.Trace("Square does not cross lon 180. left longitude is {0}, right longitude is {1}.", leftLongitude, rightLongitude);
res = i => (minLatitude <= i.InitialLocationLatitude) && (i.InitialLocationLatitude <= maxLatitude) &&
(leftLongitude <= i.InitialLocationLongitude) && (i.InitialLocationLongitude <= rightLongitude);
}
else
{
decimal leftLongitude;
decimal rightLongitude;
// b) Square crosses longitude 180. This is the more complicated case. One or two corners
// have positive longitude and the remaining have negative longitude.
if (leftCornersSameSign)
{
// Left top and left bottom corners are on the same side of longitude 180.
// The left most corner is the one with smaller longitude value.
leftLongitude = Math.Min(square.LeftTop.Longitude, square.LeftBottom.Longitude);
}
else
{
// Left top and left bottom corners are NOT on the same side of longitude 180.
// The left most corner is the one with the positive value as the negative value is on the right of longitude 180.
leftLongitude = square.LeftTop.Longitude > 0 ? square.LeftTop.Longitude : square.LeftBottom.Longitude;
}
if (rightCornersSameSign)
{
// Right top and right bottom corners are on the same side of longitude 180.
// The right most corner is the one with higher longitude value.
rightLongitude = Math.Max(square.RightTop.Longitude, square.RightBottom.Longitude);
}
else
{
// Right top and right bottom corners are NOT on the same side of longitude 180.
// The right most corner is the one with the negative value as the positive value is on the left of longitude 180.
rightLongitude = square.RightTop.Longitude < 0 ? square.RightTop.Longitude : square.RightBottom.Longitude;
}
// Note the OR operator instead of AND operator for longitude comparison.
// This is because a longitude value can not be higher than e.g. 170 and lower than e.g. -150 at the same time.
// The point is within the square if its longitude is 170 or more (up to 180) OR -150 or less (down to -180).
log.Trace("Square crosses lon 180. left longitude is {0}, right longitude is {1}.", leftLongitude, rightLongitude);
res = i => (minLatitude <= i.InitialLocationLatitude) && (i.InitialLocationLatitude <= maxLatitude) &&
((leftLongitude <= i.InitialLocationLongitude) || (i.InitialLocationLongitude <= rightLongitude));
}
}
log.Trace("(-)");
return(res);
}