Base animation duration on actual distance estimation

2 files changed, 51 insertions, 3 deletions

diff --git a/android/lib/model/src/main/kotlin/net/mullvad/mullvadvpn/model/LatLong.kt b/android/lib/model/src/main/kotlin/net/mullvad/mullvadvpn/model/LatLong.kt
index ae047130e8..d6749a16a2 100644
--- a/android/lib/model/src/main/kotlin/net/mullvad/mullvadvpn/model/LatLong.kt
+++ b/android/lib/model/src/main/kotlin/net/mullvad/mullvadvpn/model/LatLong.kt
@@ -1,11 +1,13 @@
 package net.mullvad.mullvadvpn.model
 
+import kotlin.math.cos
 import kotlin.math.pow
 import kotlin.math.sqrt
+import net.mullvad.mullvadvpn.model.Latitude.Companion.mean
 
 data class LatLong(val latitude: Latitude, val longitude: Longitude) {
 
-    fun distanceTo(other: LatLong): Float =
+    fun degreeDistanceTo(other: LatLong): Float =
         sqrt(
             latitude.distanceTo(other.latitude).pow(2f) +
                 (longitude.distanceTo(other.longitude).pow(2f))
@@ -16,6 +18,31 @@ data class LatLong(val latitude: Latitude, val longitude: Longitude) {
 
     operator fun minus(other: LatLong) =
         LatLong(latitude - other.latitude, longitude - other.longitude)
+
+    /**
+     * Calculate the distance between two points on the earth's surface using the spherical earth
+     * projected to a plane. ( This method has some drawbacks and shortcomings for extreme values
+     * closer to the Poles but should be good enough for our use case. ) Reference:
+     * https://en.wikipedia.org/wiki/Geographical_distance#Spherical_Earth_projected_to_a_plane
+     *
+     * @param other the other point to calculate the distance to.
+     * @return the estimated distance in kilometers.
+     */
+    fun seppDistanceTo(other: LatLong): Float =
+        EARTH_RADIUS *
+            sqrt(
+                latitude.distanceTo(other.latitude).toRadians().pow(2) +
+                    (cos(mean(latitude, other.latitude).value.toRadians()) *
+                            longitude.distanceTo(other.longitude).toRadians())
+                        .pow(2)
+            )
+
+    companion object {
+        // Average radius of the earth in kilometers
+        const val EARTH_RADIUS = 6371.009f
+    }
 }
 
 const val COMPLETE_ANGLE = 360f
+
+fun Float.toRadians() = this * Math.PI.toFloat() / (COMPLETE_ANGLE / 2)
diff --git a/android/lib/model/src/test/kotlin/net/mullvad/mullvadvpn/model/LatLongTest.kt b/android/lib/model/src/test/kotlin/net/mullvad/mullvadvpn/model/LatLongTest.kt
index 6644e25e82..b8608ca55c 100644
--- a/android/lib/model/src/test/kotlin/net/mullvad/mullvadvpn/model/LatLongTest.kt
+++ b/android/lib/model/src/test/kotlin/net/mullvad/mullvadvpn/model/LatLongTest.kt
@@ -2,12 +2,13 @@ package net.mullvad.mullvadvpn.model
 
 import kotlin.math.sqrt
 import org.junit.jupiter.api.Assertions.assertEquals
+import org.junit.jupiter.api.Assertions.assertTrue
 import org.junit.jupiter.api.Test
 
 class LatLongTest {
 
     @Test
-    fun `distance between two LatLong should be same as hypotenuse`() {
+    fun `degree distance between two LatLong should be same as hypotenuse`() {
         val latLong1 = LatLong(Latitude(30f), Longitude(40f))
         val latLong2 = LatLong(Latitude(-40f), Longitude(170f))
 
@@ -15,6 +16,26 @@ class LatLongTest {
         val longDiff = latLong1.longitude.distanceTo(latLong2.longitude)
         val hypotenuse = sqrt(latDiff * latDiff + longDiff * longDiff)
 
-        assertEquals(hypotenuse, latLong1.distanceTo(latLong2))
+        assertEquals(hypotenuse, latLong1.degreeDistanceTo(latLong2))
+    }
+
+    @Test
+    fun `ensure seppDistance respects lateral value`() {
+        // Malmö & New York is a shorter distance than Malmö & Johannesburg, but the degree
+        // difference is larger since they are at a higher latitude.
+
+        // Malmo 55.6050° N, 13.0038° E
+        val malmo = LatLong(Latitude(55.6050f), Longitude(13.0038f))
+
+        // New York 40.7128° N, 74.0060° W
+        val newYork = LatLong(Latitude(40.7128f), Longitude(-74.0060f))
+
+        // Johannesburg 26.2041° S, 28.0473° E
+        val johannesburg = LatLong(Latitude(-26.2041f), Longitude(28.0473f))
+
+        val malmoToNewYork = malmo.seppDistanceTo(newYork)
+        val malmoToJohannesburg = malmo.seppDistanceTo(johannesburg)
+
+        assertTrue { malmoToNewYork < malmoToJohannesburg }
     }
 }