distance between gps points

GpsDist.kt

import kotlin.math.*

interface ILatLng {
    val lat: Double
    val lon: Double
}

enum class Unit(s: String) {
    KILOMETERS("km"),
    METERS("m"),
    MILES("mi"),
    NAUTICAL_MILES("nmi"),
    FEET("ft"),
    INCHES("in"),
    RADIANS("rad"),
    DEGREES("deg")
}

//# mean earth radius - https://en.wikipedia.org/wiki/Earth_radius#Mean_radius
const val _AVG_EARTH_RADIUS_KM = 6371.0088
private val _CONVERSIONS = mapOf(
    Unit.KILOMETERS to 1.0,
    Unit.METERS to 1000.0,
    Unit.MILES to 0.621371192,
    Unit.NAUTICAL_MILES to 0.539956803,
    Unit.FEET to 3280.839895013,
    Unit.INCHES to 39370.078740158,
    Unit.RADIANS to 1 / _AVG_EARTH_RADIUS_KM,
    Unit.DEGREES to (1 / _AVG_EARTH_RADIUS_KM) * (180.0 / Math.PI)
)

fun get_avg_earth_radius(unit: Unit): Double {
    return _AVG_EARTH_RADIUS_KM * _CONVERSIONS[unit]!!
}

fun haversine(point1: ILatLng, point2: ILatLng, unit: Unit = Unit.KILOMETERS): Double {
    val lat1 = Math.toRadians(point1.lat)
    val lng1 = Math.toRadians(point1.lon)
    val lat2 = Math.toRadians(point2.lat)
    val lng2 = Math.toRadians(point2.lon)
    val lat = lat2 - lat1
    val lng = lng2 - lng1
    val d = (sin(lat * 0.5).pow(2)) + cos(lat1) * cos(lat2) * (sin(lng * 0.5).pow(2))

    return 2 * get_avg_earth_radius(unit) * asin(sqrt(d))
}

fun ILatLng.dist(that: ILatLng): Double = haversine(this, that, unit = Unit.METERS)