draw an arrow from home to space

src/main.rs

@@ -32,11 +32,20 @@ fn main() {
             global: true,
             ..Default::default()
         })
+        .insert_resource(HomeCartesian::default())
         .add_systems(Startup, (spawn_earth, spawn_camera))
-        .add_systems(Update, (close_on_esc, update_camera_offset, move_camera))
+        .add_systems(
+            Update,
+            (close_on_esc, update_camera_offset, move_camera, draw_arrow),
+        )
         .run();
 }
 
+// const RADIUS: f32 = 6378.0;
+const RADIUS: f32 = 100.0;
+const HOME_LAT: f32 = 34.2;
+const HOME_LONG: f32 = -118.45;
+
 #[derive(Debug, Resource)]
 pub struct DebugCamOffset {
     pub long: f32,
@@ -44,27 +53,53 @@ pub struct DebugCamOffset {
     pub lat: f32,
 }
 
+#[derive(Debug, Resource)]
+pub struct HomeCartesian {
+    pub pos: Vec3,
+}
+
+impl Default for HomeCartesian {
+    fn default() -> Self {
+        Self {
+            pos: polar2cart(HOME_LAT, HOME_LONG, RADIUS),
+        }
+    }
+}
+
 impl Default for DebugCamOffset {
     fn default() -> Self {
         DebugCamOffset {
-            // 500 units above los angeles
             dist: 500.0,
-            lat: 34.2,
+            lat: 0.0,
             long: -118.45,
         }
     }
 }
 
+/// From degrees lat/long to X,Y,Z (Y-up)
+fn polar2cart(lat: f32, long: f32, radius: f32) -> Vec3 {
+    let r_cos_lat = radius * lat.to_radians().cos();
+    let x = r_cos_lat * long.to_radians().sin();
+    let y = radius * lat.to_radians().sin();
+    let z = r_cos_lat * long.to_radians().cos();
+    Vec3::new(x, y, z)
+}
+
 fn spawn_earth(
     mut commands: Commands,
     mut meshes: ResMut<Assets<Mesh>>,
     mut materials: ResMut<Assets<StandardMaterial>>,
 ) {
-    let spatial_bundle = (Transform::default(), Visibility::default());
-    let mat = materials.add(StandardMaterial::default());
+    let spatial_bundle = (
+        Transform::from_rotation(Quat::from_rotation_x(90.0f32.to_radians())),
+        Visibility::default(),
+    );
+    let mat = materials.add(StandardMaterial::from_color(Color::linear_rgba(
+        0., 0., 0., 0.,
+    )));
     commands.spawn((
         spatial_bundle,
-        Mesh3d(meshes.add(Sphere::new(100.0).mesh().ico(10).unwrap())),
+        Mesh3d(meshes.add(Sphere::new(100.0).mesh().uv(32, 18))),
         MeshMaterial3d(mat),
         WireframeColor { color: BLUE.into() },
         AmbientLight {
@@ -106,13 +141,9 @@ fn move_camera(camera: Single<&mut Transform, With<SpaceCamera>>, offset: Res<De
     let origin = Vec3::ZERO;
     let north = Vec3::Y;
 
-    let mut new_xform = Transform::from_translation(origin);
-    new_xform.rotate(Quat::from_axis_angle(north, offset.long.to_radians()));
-    new_xform.rotate(Quat::from_axis_angle(
-        *xform.left(),
-        offset.lat.to_radians(),
-    ));
-    new_xform.translation += new_xform.forward() * offset.dist;
+    let pos = polar2cart(offset.lat, offset.long, offset.dist);
+    let mut new_xform = Transform::from_translation(pos);
+
     new_xform.look_at(origin, north);
 
     *xform = new_xform;
@@ -133,14 +164,14 @@ fn update_camera_offset(
                 if shifted {
                     offset.lat += 0.5;
                 } else {
-                    offset.dist += 10.0;
+                    offset.dist -= 10.0;
                 }
             }
             KeyCode::ArrowDown => {
                 if shifted {
                     offset.lat -= 0.5;
                 } else {
-                    offset.dist -= 10.0;
+                    offset.dist += 10.0;
                 }
             }
             KeyCode::KeyR => {
@@ -155,3 +186,9 @@ fn update_camera_offset(
         keys.clear_just_released(key);
     }
 }
+
+fn draw_arrow(home: Res<HomeCartesian>, mut gizmos: Gizmos) {
+    let start = home.pos;
+    let end = home.pos * 2.0;
+    gizmos.arrow(start, end, Color::linear_rgb(1.0, 1.0, 0.0));
+}