Correctly compute the radius in tiles at any given position

src/geopos.rs

@@ -64,6 +64,15 @@ impl GeoPos {
             lon: geo.longitude() as f32 / PI * 180.0,
         }
     }
+
+    /// Tile width and height in meters
+    pub fn tile_size(self, zoom: u8) -> Vec2 {
+        let pow_zoom = 2_u32.pow(zoom.into()) as f32;
+        let tile_width = EQUATOR_METERS / pow_zoom;
+        let tile_height = tile_width * self.lat.cos();
+        Vec2::new(tile_width, tile_height.abs())
+    }
 }
 
 pub const EARTH_RADIUS: f32 = 6378000.;
+pub const EQUATOR_METERS: f32 = 40_075_016.686;

src/lib.rs

@@ -166,7 +166,7 @@ fn load_next_tile(
             } else if fps > 59.5 {
                 sky.scale = Vec3::splat(sky.scale.x * 1.01)
             }
-            sky.scale = Vec3::splat(sky.scale.x.clamp(1000.0, 10000.0));
+            sky.scale = Vec3::splat(sky.scale.x.clamp(1000.0, 3000.0));
             fog.single_mut().falloff = FogFalloff::from_visibility_colors(
                 sky.scale.x, // distance in world units up to which objects retain visibility (>= 5% contrast)
                 Color::rgb(0.35, 0.5, 0.66), // atmospheric extinction color (after light is lost due to absorption by atmospheric particles)
@@ -175,13 +175,10 @@ fn load_next_tile(
         }
     }
 
-    let origin = GeoPos::from_cartesian(pos - transform.translation).to_tile_coordinates(15);
-    let (x, y) = pos.any_orthonormal_pair();
-    let radius =
-        GeoPos::from_cartesian(pos - transform.translation + x * sky.scale.x + y * sky.scale.x)
-            .to_tile_coordinates(15)
-            .0
-            - origin.0;
+    let origin = GeoPos::from_cartesian(pos - transform.translation);
+    let tile_size = origin.tile_size(15);
+    let radius = sky.scale.x / tile_size;
+    let origin = origin.to_tile_coordinates(15);
 
     tilemap.load_next(
         id,