Start Navara's camera model from a placed pose only

Navara's camera sits at the Earth's centre until it is first placed. The
model took that as the pose, so camera.height() threw while a layer
attached to a starting Navara (wildlife sightings asks for it), and
switching to Navara with that layer on rolled back to Cesium.

src/globe/navara/cameraModel.js

@@ -101,7 +101,13 @@ export function createCameraModel({
   };
   // A camera command takes the camera from whoever held it; say so first.
   const announce = () => events.commanded.raiseEvent();
-  const initial = port.read();
+  // Navara's camera sits at the Earth's centre until it is first placed: no
+  // pose yet (Cesium's camera always has one).
+  const read = () => {
+    const pose = port.read();
+    return pose && cartesian3.magnitude(pose.position) > 1 ? pose : null;
+  };
+  const initial = read();
   let state = initial
     ? copyPose(initial)
     : (() => {
@@ -216,7 +222,7 @@ export function createCameraModel({
 
   /** Reads Navara's drawn camera; called once per frame before preRender. */
   function sync() {
-    const seen = port.read();
+    const seen = read();
     if (!seen) return;
     const moved = !lastSeen || !posesNear(seen, lastSeen, 1e-6, 1e-10);
     lastSeen = copyPose(seen);

src/globe/navara/cameraModel.test.mjs

@@ -157,6 +157,21 @@ test('a camera Navara moves by itself (user input) becomes the pose', () => {
   near(camera.pose().heading, 0.3, 1e-9, 'heading');
 });
 
+test('a Navara camera not yet placed (at the Earth centre) is not the pose', () => {
+  const port = createFakePort();
+  const unplaced = {
+    position: cartesian3.create(0, 0, 0),
+    direction: cartesian3.create(0, 0, -1),
+    up: cartesian3.create(0, 1, 0),
+  };
+  port.drawn = unplaced;
+  const model = createCameraModel({ port, clock: createClock() });
+  assert.ok(Number.isFinite(model.camera.height()), 'height at start');
+  model.sync();
+  assert.ok(Number.isFinite(model.camera.height()), 'height after a sync');
+  assert.ok(model.camera.pose().cartographic, 'a place on the Earth');
+});
+
 test('missing angles default to heading 0, pitch −π/2 and roll 0', () => {
   const { camera } = setup();
   const destination = cartesian3.fromDegrees(40, 30, 20000);