Added MapTile(boundingBox:maxZoom:) (#64)

Outdooractive · Aug 12, 2024 · a8118bc · a8118bc
1 parent a2d37e2
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diff --git a/Sources/GISTools/GeoJson/BoundingBox.swift b/Sources/GISTools/GeoJson/BoundingBox.swift
@@ -600,6 +600,13 @@ extension BoundingBox {
         return nil
     }
 
+    /// `true` if the receiver crosses the anti-meridian.
+    public var crossesAntiMeridian: Bool {
+        let boundingBox = self.normalized()
+
+        return boundingBox.southWest.longitude > boundingBox.northEast.longitude
+    }
+
 }
 
 // MARK: - Helpers

diff --git a/Sources/GISTools/Other/MapTile.swift b/Sources/GISTools/Other/MapTile.swift
@@ -37,6 +37,10 @@ public struct MapTile: CustomStringConvertible, Sendable {
         ]
     }
 
+    public var siblings: [MapTile] {
+        parent.children
+    }
+
     public init(x: Int, y: Int, z: Int) {
         self.x = x
         self.y = y
@@ -52,6 +56,50 @@ public struct MapTile: CustomStringConvertible, Sendable {
         self.z = zoom
     }
 
+    // Ported from https://github.com/mapbox/tilebelt/blob/master/index.js
+    /// Initialize a tile from a bounding box.
+    /// The resulting tile will have a zoom level in `0...maxZoom`.
+    ///
+    /// - parameter boundingBox: The bounding box that the tile should completely contain
+    /// - parameter maxZoom: The maximum zoom level of the resulting tile, 0...32
+    public init(
+        boundingBox: BoundingBox,
+        maxZoom: Int = 32)
+    {
+        if boundingBox.crossesAntiMeridian {
+            self.init(x: 0, y: 0, z: 0)
+            return
+        }
+
+        let maxZoom = max(0, min(32, maxZoom))
+
+        let min = MapTile(coordinate: boundingBox.southWest, atZoom: 32)
+        let max = MapTile(coordinate: boundingBox.northEast, atZoom: 32)
+
+        var bestZ = -1
+        for z in 0 ..< maxZoom {
+            let mask = 1 << (32 - (z + 1))
+            if (min.x & mask) != (max.x & mask)
+                || (min.y & mask) != (max.y & mask)
+            {
+                bestZ = z
+                break
+            }
+        }
+        if bestZ == 0 {
+            self.init(x: 0, y: 0, z: 0)
+            return
+        }
+        if bestZ == -1 {
+            bestZ = maxZoom
+        }
+
+        self.init(
+            x: min.x >> (32 - bestZ),
+            y: min.y >> (32 - bestZ),
+            z: bestZ)
+    }
+
     public init?(string: String) {
         guard let components = string.components(separatedBy: "/").nilIfEmpty,
               components.count == 3,

diff --git a/Tests/GISToolsTests/Other/MapTileTests.swift b/Tests/GISToolsTests/Other/MapTileTests.swift
@@ -18,6 +18,25 @@ final class MapTileTests: XCTestCase {
 
     }
 
+    func testTileFromBoundingBox() throws {
+        let boundingBox1 = BoundingBox(
+            southWest: Coordinate3D(latitude: 46.5, longitude: 10.5),
+            northEast: Coordinate3D(latitude: 48.5, longitude: 11.0))
+        let boundingBox2 = BoundingBox(
+            southWest: Coordinate3D(latitude: 46.5, longitude: 10.5),
+            northEast: Coordinate3D(latitude: 48.5, longitude: 11.25))
+        let boundingBox3 = try XCTUnwrap(BoundingBox(coordinates: [Coordinate3D(latitude: 47.56, longitude: 10.22)]))
+
+        XCTAssertEqual(MapTile(boundingBox: boundingBox1), MapTile(x: 33, y: 22, z: 6))
+        XCTAssertEqual(MapTile(boundingBox: boundingBox2), MapTile(x: 8, y: 5, z: 4))
+
+        XCTAssertEqual(MapTile(boundingBox: boundingBox3), MapTile(x: 2269412997, y: 1500804469, z: 32))
+        XCTAssertEqual(MapTile(boundingBox: boundingBox3, maxZoom: 14), MapTile(x: 8657, y: 5725, z: 14))
+        XCTAssertEqual(MapTile(boundingBox: boundingBox3, maxZoom: 8), MapTile(x: 135, y: 89, z: 8))
+        XCTAssertEqual(MapTile(boundingBox: boundingBox3, maxZoom: 4), MapTile(x: 8, y: 5, z: 4))
+        XCTAssertEqual(MapTile(boundingBox: boundingBox3, maxZoom: 0), MapTile(x: 0, y: 0, z: 0))
+    }
+
     func testCenter() {
         let coordinate1 = MapTile(x: 138513, y: 91601, z: 18).centerCoordinate()
         XCTAssertEqual(coordinate1.latitude, 47.56031069944929, accuracy: 0.00001)