fix heading calculation to not return negative numbers

add sanity tests for this that test north, south, east, west to be what they should be
jillesvangurp · Oct 8, 2021 · 33fa8c3 · 33fa8c3
1 parent 32b84ed
commit 33fa8c3
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diff --git a/src/commonMain/kotlin/com/jillesvangurp/geo/GeoGeometry.kt b/src/commonMain/kotlin/com/jillesvangurp/geo/GeoGeometry.kt
@@ -1088,23 +1088,30 @@ class GeoGeometry {
         /**
          * Returns the heading from one LatLng to another LatLng as a compass direction.
          *
-         * @see https://www.igismap.com/formula-to-find-bearing-or-heading-angle-between-two-points-latitude-longitude/
+         * @see https://stackoverflow.com/questions/9457988/bearing-from-one-coordinate-to-another
          *
          * @return The heading in degrees clockwise from north.
          */
-        fun headingFromTwoPoints(from: PointCoordinates, to: PointCoordinates): Double {
-            val fromLat = toRadians(from.latitude)
-            val fromLng = toRadians(from.longitude)
-            val toLat = toRadians(to.latitude)
-            val toLng = toRadians(to.longitude)
-            val dLng = toLng - fromLng
-            val headingInRadians = atan2(
-                sin(dLng) * cos(toLat),
-                cos(fromLat) * sin(toLat) - sin(fromLat) * cos(toLat) * cos(dLng)
-            )
-            return fromRadians(headingInRadians)
-        }
+        fun headingFromTwoPoints(from: PointCoordinates, to: PointCoordinates): Double = headingFromTwoPoints(from.latitude,from.longitude,to.latitude,to.longitude)
 
+        /**
+         * Returns the heading from one LatLng to another LatLng as a compass direction.
+         *
+         * @see https://stackoverflow.com/questions/9457988/bearing-from-one-coordinate-to-another
+         *
+         * @return The heading in degrees clockwise from north.
+         */
+        fun headingFromTwoPoints(lat1: Double, lon1: Double, lat2: Double, lon2: Double): Double {
+            val latitude1: Double = toRadians(lat1)
+            val latitude2: Double = toRadians(lat2)
+            val longDiff: Double = toRadians(lon2 - lon1)
+            val y: Double = sin(longDiff) * cos(latitude2)
+            val x: Double =
+                cos(latitude1) * sin(latitude2) - sin(latitude1) * cos(
+                    latitude2
+                ) * cos(longDiff)
+            return (fromRadians(atan2(y, x)) + 360) % 360
+        }
         /**
          * @param point point
          * @return a json representation of the point

diff --git a/src/commonTest/kotlin/com/jillesvangurp/geogeometry/GeoGeometryTest.kt b/src/commonTest/kotlin/com/jillesvangurp/geogeometry/GeoGeometryTest.kt
@@ -11,6 +11,7 @@ import io.kotest.matchers.shouldBe
 import kotlinx.serialization.json.JsonElement
 import kotlinx.serialization.json.JsonObject
 import kotlin.math.absoluteValue
+import kotlin.math.roundToLong
 import kotlin.test.Test
 
 //    val bigRing = arrayOf(potsDammerPlatz, brandenBurgerGate, naturkundeMuseum, senefelderPlatz, moritzPlatz, potsDammerPlatz)
@@ -85,7 +86,10 @@ class GeoGeometryTest {
         val polygonObject = json.decodeFromString(JsonObject.serializer(), testPolygon)
         val polygon = json.decodeFromJsonElement(Geometry.serializer(), polygonObject) as Geometry.Polygon
         val serializedPolygonObject = json.encodeToJsonElement(Geometry.serializer(), polygon)
-        jsonPretty.encodeToString(JsonElement.serializer(), serializedPolygonObject) shouldBe jsonPretty.encodeToString(JsonElement.serializer(), polygonObject)
+        jsonPretty.encodeToString(JsonElement.serializer(), serializedPolygonObject) shouldBe jsonPretty.encodeToString(
+            JsonElement.serializer(),
+            polygonObject
+        )
     }
 
     @Test
@@ -112,7 +116,40 @@ class GeoGeometryTest {
         println(FeatureCollection(features))
     }
 
-    val testPolygon = """
+    @Test
+    fun headingFromTwoPoints() {
+        GeoGeometry.headingFromTwoPoints(
+            doubleArrayOf(13.0, 52.0),
+            doubleArrayOf(14.0, 53.0)
+        ).roundToLong() shouldBe 31
+        GeoGeometry.headingFromTwoPoints(
+            doubleArrayOf(14.0, 53.0),
+            doubleArrayOf(13.0, 52.0)
+        ).roundToLong() shouldBe 212
+    }
+
+    @Test
+    fun headingFromTwoPointsShouldBeBetweenZeroAnd360() {
+        GeoGeometry.headingFromTwoPoints(
+            doubleArrayOf(13.0, 52.0),
+            doubleArrayOf(13.0, 52.0001)
+        ).roundToLong() shouldBe 0
+        GeoGeometry.headingFromTwoPoints(
+            doubleArrayOf(12.999, 52.0),
+            doubleArrayOf(13.0, 52.0)
+        ).roundToLong() shouldBe 90
+        GeoGeometry.headingFromTwoPoints(
+            doubleArrayOf(13.0, 52.0001),
+            doubleArrayOf(13.0, 52.0)
+        ).roundToLong() shouldBe 180
+        GeoGeometry.headingFromTwoPoints(
+            doubleArrayOf(13.0, 52.0),
+            doubleArrayOf(12.999, 52.0)
+        ).roundToLong() shouldBe 270
+    }
+}
+
+val testPolygon = """
         {
         "coordinates": [
           [
@@ -158,7 +195,7 @@ class GeoGeometryTest {
       }
     """.trimIndent()
 
-    val badGeo = """
+val badGeo = """
 {
               "coordinates": [
                 [
@@ -1278,4 +1315,3 @@ class GeoGeometryTest {
               "type": "Polygon"
             }        
     """.trimIndent()
-}
diff --git a/src/jvmTest/kotlin/com/jillesvangurp/geogeometry/GeoGeometryJvmTest.kt b/src/jvmTest/kotlin/com/jillesvangurp/geogeometry/GeoGeometryJvmTest.kt
@@ -869,15 +869,5 @@ class GeoGeometryJvmTest {
         MatcherAssert.assertThat("should contain the point", polygonContains(point, polygon))
     }
 
-    @Test
-    fun headingFromTwoPoints() {
-        GeoGeometry.headingFromTwoPoints(
-            doubleArrayOf(13.0, 52.0),
-            doubleArrayOf(14.0, 53.0)
-        ) shouldBeApproximately 30.93571619
-        GeoGeometry.headingFromTwoPoints(
-            doubleArrayOf(14.0, 53.0),
-            doubleArrayOf(13.0, 52.0)
-        ) shouldBeApproximately -148.270892801
-    }
+
 }