feat(preview): add low poly vehicle library

scripts/lib/cesium-preview.js

@@ -37,7 +37,7 @@
     const viewer = createViewer();
     setLoadingMessage("Loading model", config.glbName || "");
     const assets = await loadSceneAssets(viewer, metadata, placement);
-    const cruise = addVehicleCruises(viewer, routeData, config.vehicleModelName);
+    const cruise = addVehicleCruises(viewer, routeData, config.vehicleModelNames, config.vehicleModelName);
     const cameras = createCameraPresets(viewer, metadata, placement, cruise);
 
     buildAssetToggles(assets);
@@ -422,7 +422,7 @@
     return stopFollow;
   }
 
-  function addVehicleCruises(viewer, routeData, vehicleModelName) {
+  function addVehicleCruises(viewer, routeData, vehicleModelNames, fallbackVehicleModelName) {
     const segments = ((routeData && (routeData.routes || routeData.segments)) || [])
       .filter((segment) => segment.coordinates && segment.coordinates.length >= 2)
       .slice(0, 5);
@@ -436,7 +436,8 @@
     viewer.clock.shouldAnimate = segments.length > 0;
 
     const vehicles = segments.map((segment, index) => {
-      const vehicle = addCruiseVehicle(viewer, segment, index, start, speed, vehicleModelName);
+      const vehicle = addCruiseVehicle(viewer, segment, index, start, speed,
+        selectedVehicleModelName(vehicleModelNames, fallbackVehicleModelName));
       const option = document.createElement("option");
       option.value = String(index);
       option.textContent = routeLabel(segment, index);
@@ -450,6 +451,14 @@
     };
   }
 
+  function selectedVehicleModelName(modelNames, fallbackModelName) {
+    const choices = Array.isArray(modelNames) && modelNames.length
+      ? modelNames
+      : [fallbackModelName];
+    const usable = choices.filter(Boolean);
+    return usable[Math.floor(Math.random() * usable.length)] || "";
+  }
+
   function addCruiseVehicle(viewer, segment, index, start, speed, vehicleModelName) {
     const route = prepareRoute(segment);
     const positions = new Cesium.CallbackProperty((time, result) => {
@@ -482,9 +491,10 @@
       orientation: routeOrientation(route, start, speed, 0.0),
       model: {
         uri: vehicleModelName,
-        scale: 1.0,
-        minimumPixelSize: 24,
-        maximumScale: 80
+        // Keep the library's world scale visible. A minimum screen size made
+        // long trucks balloon in overview and at intersections.
+        scale: 0.72,
+        minimumPixelSize: 0
       }
     });
     return {