Add functions that specify UTM zone for conversion

README.md

@@ -66,3 +66,16 @@ let utmCoordinate = UTMCoordinate(northing: 7034313, easting: 569612, zone: 32,
 let datum = UTMDatum(equitorialRadius: 6378137, polarRadius: 6356752.3142)
 let coordinate = utmCoordinate.coordinate(datum: datum)
 ```
+
+### UTM Zone
+
+It is possible to specify the UTM zone for conversion, e.g. if you want consistent UTM coordinates at a border of two zones.
+
+```swift
+import CoreLocation
+import UTMConversion
+
+let location = CLLocation(latitude: 51.357402, longitude: 12.002263)
+let utmCoordinateInZone33 = utmCoordinate.coordinate() // Coordinate is in 33, but at the border to 32.
+let utmCoordinateInZone32 = utmCoordinate.coordinate(zone: 32)
+```

Sources/UTMConversion/CLLocation+UTMCoordinate.swift

@@ -14,5 +14,17 @@ public extension CLLocation {
         let zone = coordinate.zone
         return TMCoordinate(coordinate: coordinate, centralMeridian: zone.centralMeridian, datum: datum).utmCoordinate(zone: zone, hemisphere: coordinate.hemisphere)
     }
-
+
+    /**
+        Calculates the UTM coordinate of the receiver
+
+        - Parameter zone: The UTM zone to use
+        - Parameter datum: The datum to use, defaults to WGS84 which should be fine for most applications
+
+     */
+    func utmCoordinate(zone: UTMGridZone, datum: UTMDatum = UTMDatum.wgs84) -> UTMCoordinate {
+        let coordinate = self.coordinate
+        return TMCoordinate(coordinate: coordinate, centralMeridian: zone.centralMeridian, datum: datum).utmCoordinate(zone: zone, hemisphere: coordinate.hemisphere)
+    }
+
 }

Sources/UTMConversion/CLLocationCoordinate2D+UTMCoordinate.swift

@@ -14,8 +14,18 @@ public extension CLLocationCoordinate2D {
         let zone = self.zone
         return TMCoordinate(coordinate: self, centralMeridian: zone.centralMeridian, datum: datum).utmCoordinate(zone: zone, hemisphere: hemisphere)
     }
-
-
+
+    /**
+     Calculates the UTM coordinate of the receiver
+
+     - Parameter zone: The UTM zone to use
+     - Parameter datum: The datum to use, defaults to WGS84 which should be fine for most applications
+
+     */
+    func utmCoordinate(zone: UTMGridZone, datum: UTMDatum = UTMDatum.wgs84) -> UTMCoordinate {
+        TMCoordinate(coordinate: self, centralMeridian: zone.centralMeridian, datum: datum).utmCoordinate(zone: zone, hemisphere: hemisphere)
+    }
+
     /**
      The UTM grid zone
      */

Tests/UTMConversionTests/UTMConversionTests.swift

@@ -97,6 +97,30 @@ class UTMConversionTests: XCTestCase {
         let oslo = osloUTM.location(datum: UTMDatum(equitorialRadius: 6378137, polarRadius: 6356752.3142))
         XCTAssertEqual(oslo.coordinate.latitude, 59.912814611065265)
         XCTAssertEqual(oslo.coordinate.longitude, 10.760192985178369)
+
+    }
+
+    func testCustomZone() {
+        // Coordinate located in UTM zone 33
+        let lat = 51.357402
+        let lon = 12.002263
+
+        // echo "12.002263 51.357402" | proj -f "%.5f" +proj=utm +zone=32 +datum=WGS84 +units=m +no_defs
+        let northing32 = 5693849.66049
+        let easting32 = 709023.99157
+        let zone: UTMGridZone = 32
+
+        let neumarkt2D = CLLocationCoordinate2D(latitude: lat, longitude: lon).utmCoordinate(zone: zone)
+        XCTAssertEqual(neumarkt2D.northing, northing32, accuracy: 0.0001)
+        XCTAssertEqual(neumarkt2D.easting, easting32, accuracy: 0.0001)
+        XCTAssertEqual(neumarkt2D.zone, zone)
+        XCTAssertEqual(neumarkt2D.hemisphere, .northern)
+
+        let neumarkt = CLLocation(latitude: lat, longitude: lon).utmCoordinate(zone: zone)
+        XCTAssertEqual(neumarkt.northing, northing32, accuracy: 0.0001)
+        XCTAssertEqual(neumarkt.easting, easting32, accuracy: 0.0001)
+        XCTAssertEqual(neumarkt.zone, zone)
+        XCTAssertEqual(neumarkt.hemisphere, .northern)
     }
 }