public static Expression <Func <T, double> > CalculateDistanceFrom <T>(double originLatitude, double originLongitude, string latitudePropertyName, string longitudePropertyName, DistanceUnit distanceUnit)
{
var earthsRadiusConstantExpression = Expression.Constant(GeoCalculator.GetRadius(distanceUnit));
var inputExpression = Expression.Parameter(typeof(T), "x");
var originLatitudeExpression = Expression.Constant(originLatitude);
var originLongitudeExpression = Expression.Constant(originLongitude);
var destinationLatitudeExpression = Expression.Convert(Expression.Property(inputExpression, latitudePropertyName), typeof(double));
var destinationLongitudeExpression = Expression.Convert(Expression.Property(inputExpression, longitudePropertyName), typeof(double));
if (originLatitude < -90 || originLatitude > 90 || originLongitude < -180 || originLongitude > 180)
{
return(Expression.Lambda <Func <T, double> >(Expression.Constant(-1.0), inputExpression));
}
return(Expression.Lambda <Func <T, double> >(
Expression.Multiply(
earthsRadiusConstantExpression,
Expression.Multiply(
Expression.Constant(2.0),
Expression.Call(_asin,
// MIN isn't supported in SQL
// Tested all (4B+) combinations of valid Lat/Long and calculation was never greater than 1
//Expression.Call(_min,
// Expression.Constant(1.0),
Expression.Call(_sqrt,
Expression.Add(
Expression.Call(_pow,
Expression.Call(_sin,
Expression.Divide(
originLatitudeExpression.DiffRadiansExpression(destinationLatitudeExpression),
Expression.Constant(2.0)
)
),
Expression.Constant(2.0)
),
Expression.Multiply(
Expression.Call(_cos, originLatitudeExpression.ToRadiansExpression()),
Expression.Multiply(
Expression.Call(_cos, destinationLatitudeExpression.ToRadiansExpression()),
Expression.Call(_pow,
Expression.Call(_sin,
Expression.Divide(
originLongitudeExpression.DiffRadiansExpression(destinationLongitudeExpression),
Expression.Constant(2.0)
)
),
Expression.Constant(2.0)
)
)
)
)
)
//)
)
)
),
inputExpression));
}
