Added parentat method.

src/TilesMath/Tile.cs

@@ -67,6 +67,26 @@ public Tile? Parent
         }
     }
 
+    /// <summary>
+    /// Returns the parent tile at the given zoom.
+    /// </summary>
+    /// <param name="zoom"></param>
+    /// <returns></returns>
+    /// <exception cref="ArgumentOutOfRangeException"></exception>
+    public Tile ParentAt(int zoom)
+    {
+        if (zoom < 0)
+            throw new ArgumentOutOfRangeException(nameof(zoom),
+                "Zoom has to be positive");
+        if (zoom == this.Zoom) return this;
+        if (zoom > this.Zoom) throw new ArgumentOutOfRangeException(nameof(zoom),
+            "A parent tile should have a lower zoom");
+
+        var x = this.X >> (this.Zoom - zoom);
+        var y = this.Y >> (this.Zoom - zoom);
+        return Tile.Create(x, y, zoom);
+    }
+
     /// <summary>
     /// The children.
     /// </summary>
@@ -100,8 +120,8 @@ public IEnumerable<Tile> ChildrenAtZoom(int zoom, Func<Tile, bool>? exclude = nu
 
         foreach (var childOneLevelLess in this.ChildrenAtZoom(zoom - 1))
         {
-            if (exclude != null && !exclude(childOneLevelLess)) continue;
-
+            if (exclude != null && !exclude(childOneLevelLess)) continue;
+
             foreach (var child in childOneLevelLess.Children)
             {
                 if (exclude == null || !exclude(child)) yield return child;

src/TilesMath/TilesMath.csproj

@@ -4,7 +4,7 @@
     <TargetFramework>net6.0</TargetFramework>
     <ImplicitUsings>enable</ImplicitUsings>
     <Nullable>enable</Nullable>
-    <PackageVersion>0.0.9</PackageVersion>
+    <PackageVersion>0.0.10</PackageVersion>
     <Title>TilesMath</Title>
     <Authors>ANYWAYS BV</Authors>
     <Description>A tiny library for tiles math.</Description>

test/TilesMath.Tests/TileTests.cs

@@ -0,0 +1,31 @@
+namespace TilesMath.Tests;
+
+public class TileTests
+{
+    [Fact]
+    public void Tile_ParentAt_OneZoomUp_ShouldEqualParent()
+    {
+        var tile = Tile.Create(1025, 4511, 14);
+
+        var parent = tile.Parent ?? throw new Exception("No parent");
+        Assert.Equal(parent, tile.ParentAt(tile.Zoom - 1));
+    }
+
+    [Fact]
+    public void Tile_ParentAt_TwoZoomsUp_ShouldEqualParentOfParent()
+    {
+        var tile = Tile.Create(1025, 4511, 14);
+
+        var parent = tile.Parent?.Parent ?? throw new Exception("No parent");
+        Assert.Equal(parent, tile.ParentAt(tile.Zoom - 2));
+    }
+
+    [Fact]
+    public void Tile_ParentAt_5ZoomsUp_ShouldEqual5thParentUp()
+    {
+        var tile = Tile.Create(1025, 4511, 14);
+
+        var parent = tile.Parent?.Parent?.Parent?.Parent?.Parent ?? throw new Exception("No parent");
+        Assert.Equal(parent, tile.ParentAt(tile.Zoom - 5));
+    }
+}