fix svalbard and norway

longitude meridian was wrong for the exceptions svalbard test case now passes
jillesvangurp · Nov 14, 2023 · 4523f5e · 4523f5e
1 parent 0f155b1
commit 4523f5e
Show file tree

Hide file tree

Showing 2 changed files with 47 additions and 35 deletions.
diff --git a/src/commonMain/kotlin/com/jillesvangurp/geo/utm.kt b/src/commonMain/kotlin/com/jillesvangurp/geo/utm.kt
@@ -213,36 +213,46 @@ private fun getLatitudeZoneLetter(latLong: PointCoordinates): Char {
 private fun getLongitudeZone(latLong: PointCoordinates): Int {
 
     // UPS longitude zones
-    if (isNorthPolar(latLong) || isSouthPolar(latLong)) {
-        return if (latLong.longitude < 0.0) {
+    val longitude = latLong.longitude
+    return if (isNorthPolar(latLong) || isSouthPolar(latLong)) {
+         if (longitude < 0.0) {
             30
         } else {
             31
         }
-    }
-    val latitudeZone: Char = getLatitudeZoneLetter(latLong)
-    // X latitude exceptions
-    if (latitudeZone == 'X' && latLong.longitude > 0.0 && latLong.longitude < 42.0) {
-        if (latLong.longitude < 9.0) {
-            return 31
-        }
-        if (latLong.longitude < 21.0) {
-            return 33
-        }
-        return if (latLong.longitude < 33.0) {
-            35
-        } else {
-            37
+    } else {
+        val latitudeZone: Char = getLatitudeZoneLetter(latLong)
+        when {
+            latitudeZone == 'X' && longitude > 0.0 && longitude < 42.0 -> {
+            // X latitude exceptions
+                when {
+                    longitude < 9.0 -> {
+                        31
+                    }
+                    longitude < 21.0 -> {
+                        33
+                    }
+                    longitude < 33.0 -> {
+                        35
+                    }
+                    else -> {
+                        37
+                    }
+                }
+            }
+            latitudeZone == 'V' && longitude > 0.0 && longitude < 12.0 -> {
+            // V latitude exceptions
+                if (longitude < 3.0) {
+                    31
+                } else {
+                    32
+                }
+            }
+            else -> {
+                ((longitude + 180) / 6).toInt() + 1
+            }
         }
     }
-    // V latitude exceptions
-    return if (latitudeZone == 'V' && latLong.longitude > 0.0 && latLong.longitude < 12.0) {
-        if (latLong.longitude < 3.0) {
-            31
-        } else {
-            32
-        }
-    } else ((latLong.longitude + 180) / 6).toInt() + 1
 }
 
 /**
@@ -258,15 +268,20 @@ private fun getCentralMeridian(longitudeZone: Int, latitudeZone: Char): Double {
         return 0.0
     }
     // X latitude zone exceptions
-    if (latitudeZone == 'X' && longitudeZone > 31 && longitudeZone <= 37) {
-        return toRadians((longitudeZone - 1) * 6 - 180 + 4.5)
+    // Svalbard exceptions for 'X' latitude zone
+    if (latitudeZone == 'X') {
+        when (longitudeZone) {
+            31 -> return toRadians(9.0)
+            33 -> return toRadians(15.0)
+            35 -> return toRadians(27.0)
+            37 -> return toRadians(33.0)
+        }
     }
     // V latitude zone exceptions
-    if (longitudeZone == 'V'.code) {
-        if (latitudeZone.code == 31) {
-            return 1.5
-        } else if (latitudeZone.code == 32) {
-            return 7.5
+    if (latitudeZone == 'V') {
+        when (longitudeZone) {
+            31 -> return toRadians(3.0)
+            32 -> return toRadians(9.0)
         }
     }
     return toRadians(((longitudeZone - 1) * 6 - 180 + 3).toDouble())

diff --git a/src/commonTest/kotlin/com/jillesvangurp/geogeometry/UTMTest.kt b/src/commonTest/kotlin/com/jillesvangurp/geogeometry/UTMTest.kt
@@ -31,10 +31,6 @@ val testCasses = listOf(
         name = "Svalbard Museum",
         point = doubleArrayOf(15.652313, 78.222378),
         utmString = "33X 514863.281 8683270.114",
-        // FIXME either our math is wrong or the website is wrong.
-        // may be related to svalbard exceptions: https://gis.stackexchange.com/questions/2561/what-was-the-rationale-for-the-non-standard-utm-zones-near-norway
-        include = false,
-        notes = "off by 34 km for the easting and 57 for the northing relative to https://coordinates-converter.com. At this point not clear which is right."
     ),
     TestCase(
         "Oslo, City Hall",
@@ -281,6 +277,7 @@ class UTMTest {
                         }
                     }
                 } else {
+                    // reserve for test cases that aren't working
                     println("skipping ${testCase.name} because ${testCase.notes}")
                 }
             }