Always include the m value of Coordinate3D in JSON

README.md

@@ -16,7 +16,7 @@ This package requires Swift 5.10 or higher (at least Xcode 14), and compiles on
 
 ```swift
 dependencies: [
-    .package(url: "https://github.com/Outdooractive/gis-tools", from: "1.6.0"),
+    .package(url: "https://github.com/Outdooractive/gis-tools", from: "1.7.0"),
 ],
 targets: [
     .target(name: "MyTarget", dependencies: [
@@ -36,6 +36,8 @@ targets: [
 - Includes many spatial algorithms (ported from turf.js), and more to come
 - Has a helper for working with x/y/z map tiles (center/bounding box/resolution/…)
 - Can encode/decode Polylines
+- Pure Swift without external dependencies
+- Swift 6 ready
 
 ## Usage
 
@@ -297,7 +299,10 @@ var altitude: CLLocationDistance?
 /// The GeoJSON specification doesn't specifiy the meaning of this value,
 /// and it doesn't guarantee that parsers won't ignore or discard it. See
 /// https://datatracker.ietf.org/doc/html/rfc7946#section-3.1.1.
-/// - Important: `asJson` will output `m` only if the coordinate also has an `altitude`.
+/// - Important: The JSON for a coordinate will contain a `null` altitude value
+///              if `altitude` is `nil` so that `m` won't get lost (since it is
+///              the 4th value).
+///              This might lead to compatibilty issues with other GeoJSON readers.
 var m: Double?
 
 /// Alias for longitude

Sources/GISTools/GeoJson/Coordinate3D.swift

@@ -36,7 +36,8 @@ public struct Coordinate3D:
     /// The GeoJSON specification doesn't specifiy the meaning of this value,
     /// and it doesn't guarantee that parsers won't ignore or discard it. See
     /// [chapter 3.1.1 in the spec](https://datatracker.ietf.org/doc/html/rfc7946#section-3.1.1).
-    /// - Important: ``asJson`` will output `m` only if the coordinate also has an ``altitude``.
+    /// - Important: ``asJson`` will output a `null` altitude value if ``altitude`` is `nil` so that
+    ///              `m` won't get lost. This might lead to compatibilty issues with other GeoJSON readers.
     public var m: Double?
 
     /// Alias for longitude
@@ -350,42 +351,41 @@ extension Coordinate3D: GeoJsonReadable {
     /// - Note: The [GeoJSON spec](https://datatracker.ietf.org/doc/html/rfc7946)
     ///         uses CRS:84 that specifies coordinates in longitude/latitude order.
     /// - Important: The third value will always be ``altitude``, the fourth value
-    ///              will be ``m`` if it exists.
+    ///              will be ``m`` if it exists. ``altitude`` can be a JSON `null` value.
     /// - important: The source is expected to be in EPSG:4326.
     public init?(json: Any?) {
-        guard let pointArray = json as? [Double],
-              pointArray.count >= 2
+        guard let pointArray = json as? [Double?],
+              pointArray.count >= 2,
+              let pLongitude = pointArray[0],
+              let pLatitude = pointArray[1]
         else { return nil }
 
-        if pointArray.count == 2 {
-            self.init(latitude: pointArray[1], longitude: pointArray[0])
-        }
-        else if pointArray.count == 3 {
-            self.init(latitude: pointArray[1], longitude: pointArray[0], altitude: pointArray[2])
-        }
-        else {
-            self.init(latitude: pointArray[1], longitude: pointArray[0], altitude: pointArray[2], m: pointArray[3])
-        }
+        let pAltitude: CLLocationDistance? = if pointArray.count >= 3 { pointArray[2] } else { nil }
+        let pM: Double? = if pointArray.count >= 4 { pointArray[3] } else { nil }
+
+        self.init(latitude: pLatitude, longitude: pLongitude, altitude: pAltitude, m: pM)
     }
 
     /// Dump the coordinate as a JSON object.
     ///
-    /// - Important: The output array will contain ``m`` only if this coordinate
-    ///              also contains ``altitude`` to prevent any disambiguity.
+    /// - Important: The result JSON object will have a `null` value for the altitude
+    ///              if the ``altitude`` is `nil` and ``m`` exists.
     /// - important: Always projected to EPSG:4326, unless the coordinate has no SRID.
-    public var asJson: [Double] {
-        var result: [Double] = (projection == .epsg4326 || projection == .noSRID
+    public var asJson: [Double?] {
+        var result: [Double?] = (projection == .epsg4326 || projection == .noSRID
             ? [longitude, latitude]
             : [longitudeProjected(to: .epsg4326), latitudeProjected(to: .epsg4326)])
 
         if let altitude {
             result.append(altitude)
-
-            // We can't add `m` if we don't have an altitude
             if let m {
                 result.append(m)
             }
         }
+        else if let m {
+            result.append(nil)
+            result.append(m)
+        }
 
         return result
     }
@@ -432,7 +432,7 @@ extension Sequence<Coordinate3D> {
     /// Returns all elements as an array of JSON objects
     ///
     /// - important: Always projected to EPSG:4326, unless the coordinate has no SRID.
-    public var asJson: [[Double]] {
+    public var asJson: [[Double?]] {
         self.map(\.asJson)
     }
 
@@ -442,6 +442,8 @@ extension Sequence<Coordinate3D> {
 
 extension Coordinate3D: Equatable {
 
+    /// Coordinates are regarded as equal when they are within a few μm from each other.
+    /// See ``GISTool.equalityDelta``.
     public static func == (
         lhs: Coordinate3D,
         rhs: Coordinate3D)

Sources/GISTools/GeoJson/GeoJsonCodable.swift

@@ -234,8 +234,8 @@ extension KeyedDecodingContainer where Key == GeoJsonCodingKey {
 
 extension UnkeyedDecodingContainer {
 
-    fileprivate mutating func decodeGeoJsonArray() -> [Any] {
-        var result: [Any] = []
+    fileprivate mutating func decodeGeoJsonArray() -> [Any?] {
+        var result: [Any?] = []
 
         while !isAtEnd {
             // Again, order is important
@@ -254,6 +254,9 @@ extension UnkeyedDecodingContainer {
             else if let decoded = try? decode(Float.self) {
                 result.append(decoded)
             }
+            else if let isNil = try? decodeNil(), isNil {
+                result.append(nil)
+            }
             else if var decoded = try? nestedUnkeyedContainer() {
                 result.append(decoded.decodeGeoJsonArray())
             }

Tests/GISToolsTests/GeoJson/CoordinateTests.swift

@@ -38,13 +38,24 @@ final class CoordinateTests: XCTestCase {
         XCTAssertEqual(String(data: coordinateData, encoding: .utf8), "[10,15]")
     }
 
+    func testEncodableNull() throws {
+        let coordinateM = Coordinate3D(latitude: 15.0, longitude: 10.0, altitude: nil, m: 1234)
+        let coordinateZ = Coordinate3D(latitude: 15.0, longitude: 10.0, altitude: 500.0, m: nil)
+
+        let coordinateDataM = try JSONEncoder().encode(coordinateM)
+        let coordinateDataZ = try JSONEncoder().encode(coordinateZ)
+
+        XCTAssertEqual(String(data: coordinateDataM, encoding: .utf8), "[10,15,null,1234]")
+        XCTAssertEqual(String(data: coordinateDataZ, encoding: .utf8), "[10,15,500]")
+    }
+
     func testEncodable3857() throws {
         let coordinate = Coordinate3D(latitude: 15.0, longitude: 10.0).projected(to: .epsg3857)
         let coordinateData = try JSONEncoder().encode(coordinate)
         let decodedCoordinate = try JSONDecoder().decode(Coordinate3D.self, from: coordinateData)
 
-        XCTAssertEqual(Double(decodedCoordinate.asJson[0]), 10.0, accuracy: 0.000001)
-        XCTAssertEqual(Double(decodedCoordinate.asJson[1]), 15.0, accuracy: 0.000001)
+        XCTAssertEqual(Double(decodedCoordinate.asJson[0]!), 10.0, accuracy: 0.000001)
+        XCTAssertEqual(Double(decodedCoordinate.asJson[1]!), 15.0, accuracy: 0.000001)
     }
 
     func testDecodable() throws {
@@ -54,4 +65,40 @@ final class CoordinateTests: XCTestCase {
         XCTAssertEqual(decodedCoordinate.asJson, [10.0, 15.0])
     }
 
+    func testDecodableInvalid() throws {
+        let coordinateData1 =  try XCTUnwrap("[10]".data(using: .utf8))
+        XCTAssertThrowsError(try JSONDecoder().decode(Coordinate3D.self, from: coordinateData1))
+
+        let coordinateData2 =  try XCTUnwrap("[10,]".data(using: .utf8))
+        XCTAssertThrowsError(try JSONDecoder().decode(Coordinate3D.self, from: coordinateData2))
+
+        let coordinateData3 =  try XCTUnwrap("[null,null]".data(using: .utf8))
+        XCTAssertThrowsError(try JSONDecoder().decode(Coordinate3D.self, from: coordinateData3))
+
+        let coordinateData4 =  try XCTUnwrap("[]".data(using: .utf8))
+        XCTAssertThrowsError(try JSONDecoder().decode(Coordinate3D.self, from: coordinateData4))
+
+        let coordinateData5 =  try XCTUnwrap("[,15]".data(using: .utf8))
+        XCTAssertThrowsError(try JSONDecoder().decode(Coordinate3D.self, from: coordinateData5))
+    }
+
+    func testDecodableInvalidNull() throws {
+        let coordinateDataM =  try XCTUnwrap("[10,null,null,1234]".data(using: .utf8))
+        XCTAssertThrowsError(try JSONDecoder().decode(Coordinate3D.self, from: coordinateDataM))
+    }
+
+    func testDecodableNull() throws {
+        let coordinateDataM =  try XCTUnwrap("[10,15,null,1234]".data(using: .utf8))
+        let coordinateDataZ =  try XCTUnwrap("[10,15,500]".data(using: .utf8))
+        let coordinateDataZM =  try XCTUnwrap("[10,15,500,null]".data(using: .utf8))
+
+        let decodedCoordinateM = try JSONDecoder().decode(Coordinate3D.self, from: coordinateDataM)
+        let decodedCoordinateZ = try JSONDecoder().decode(Coordinate3D.self, from: coordinateDataZ)
+        let decodedCoordinateZM = try JSONDecoder().decode(Coordinate3D.self, from: coordinateDataZM)
+
+        XCTAssertEqual(decodedCoordinateM.asJson, [10.0, 15.0, nil, 1234])
+        XCTAssertEqual(decodedCoordinateZ.asJson, [10.0, 15.0, 500])
+        XCTAssertEqual(decodedCoordinateZM.asJson, [10.0, 15.0, 500])
+    }
+
 }