Fixed numeric instability.

anyways-open · Nov 15, 2023 · 027348a · 027348a
1 parent 779f644
commit 027348a
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Showing 3 changed files with 79 additions and 47 deletions.
diff --git a/src/TilesMath/TileExtensions.cs b/src/TilesMath/TileExtensions.cs
@@ -130,66 +130,87 @@ private static IEnumerable<Tile> EnumerateTilesForLineSegment((double longitude,
             yield return tile;
 
             // determine to change x or y.
+            var xDiff = point2Tile.Value.X - tileX;
+            var yDiff = point2Tile.Value.Y - tileY;
 
             // if y at the next x is inside the current tile range (miny, maxy), we step x.
-            if (tileX != point2Tile.Value.X)
+            if (xDiff > 0)
             {
-                if (point2Tile.Value.X > tileX)
+                if (yDiff == 0)
                 {
-                    // try to move right.
-                    var nextLongitude = tile.Boundaries.Right;
-                    var latitude = GetY(nextLongitude);
-
-                    if (latitude <= tile.Boundaries.Top &&
-                        latitude >= tile.Boundaries.Bottom)
-                    {
-                        tileX += 1;
-                        continue;
-                    }
+                    tileX += 1;
+                    continue;
                 }
-                if (point2Tile.Value.X < tileX)
+
+                // try to move right.
+                var nextLongitude = tile.Boundaries.Right;
+                var latitude = GetY(nextLongitude);
+
+                if (latitude <= tile.Boundaries.Top &&
+                    latitude >= tile.Boundaries.Bottom)
                 {
-                    // try to move left.
-                    var nextLongitude = tile.Boundaries.Left;
-                    var latitude = GetY(nextLongitude);
-
-                    if (latitude <= tile.Boundaries.Top &&
-                        latitude >= tile.Boundaries.Bottom)
-                    {
-                        tileX -= 1;
-                        continue;
-                    }
+                    tileX += 1;
+                    continue;
+                }
+            }
+            if (xDiff < 0)
+            {
+                if (yDiff == 0)
+                {
+                    tileX -= 1;
+                    continue;
+                }
+
+                // try to move left.
+                var nextLongitude = tile.Boundaries.Left;
+                var latitude = GetY(nextLongitude);
+
+                if (latitude <= tile.Boundaries.Top &&
+                    latitude >= tile.Boundaries.Bottom)
+                {
+                    tileX -= 1;
+                    continue;
                 }
             }
 
             // if x at the next y is inside the current tile range (minx, maxx), we step y.
-            if (tileY != point2Tile.Value.Y)
+            if (yDiff > 0)
             {
-                if (point2Tile.Value.Y > tileY)
+                if (xDiff == 0)
                 {
-                    // try to move down.
-                    var nextLatitude = tile.Boundaries.Bottom;
-                    var longitude = GetX(nextLatitude);
-
-                    if (longitude >= tile.Boundaries.Left &&
-                        longitude <= tile.Boundaries.Right)
-                    {
-                        tileY += 1;
-                        continue;
-                    }
+                    tileY += 1;
+                    continue;
                 }
-                if (point2Tile.Value.Y < tileY)
+
+                // try to move down.
+                var nextLatitude = tile.Boundaries.Bottom;
+                var longitude = GetX(nextLatitude);
+
+                if (longitude >= tile.Boundaries.Left &&
+                    longitude <= tile.Boundaries.Right)
+                {
+                    tileY += 1;
+                    continue;
+                }
+            }
+
+            if (yDiff < 0)
+            {
+                if (xDiff == 0)
+                {
+                    tileY -= 1;
+                    continue;
+                }
+
+                // try to move up.
+                var nextLatitude = tile.Boundaries.Top;
+                var longitude = GetX(nextLatitude);
+
+                if (longitude >= tile.Boundaries.Left &&
+                    longitude <= tile.Boundaries.Right)
                 {
-                    // try to move up.
-                    var nextLatitude = tile.Boundaries.Top;
-                    var longitude = GetX(nextLatitude);
-
-                    if (longitude >= tile.Boundaries.Left &&
-                        longitude <= tile.Boundaries.Right)
-                    {
-                        tileY -= 1;
-                        continue;
-                    }
+                    tileY -= 1;
+                    continue;
                 }
             }
         }

diff --git a/src/TilesMath/TilesMath.csproj b/src/TilesMath/TilesMath.csproj
@@ -4,7 +4,7 @@
     <TargetFramework>net6.0</TargetFramework>
     <ImplicitUsings>enable</ImplicitUsings>
     <Nullable>enable</Nullable>
-    <PackageVersion>0.0.8</PackageVersion>
+    <PackageVersion>0.0.9</PackageVersion>
     <Title>TilesMath</Title>
     <Authors>ANYWAYS BV</Authors>
     <Description>A tiny library for tiles math.</Description>

diff --git a/test/TilesMath.Tests/TileStaticTests.cs b/test/TilesMath.Tests/TileStaticTests.cs
@@ -153,4 +153,15 @@ public void Tile_BetweenLine_WhenLineToNorthEast_TwoTileHop_ShouldEnumerateTwoTi
         Assert.Equal(8412, tiles[4].X);
         Assert.Equal(5464, tiles[4].Y);
     }
+
+    [Fact]
+    public void Tile_BelowTile_Regression1()
+    {
+        var tiles = Tile.BelowLine(new (double longitude, double latitude)[]
+        {
+            (-38.342295887706044, -4.0837899501379491),
+            (-38.34228515625, -4.0834527720386173)
+        }, 14).ToList();
+
+    }
 }