diff --git a/demos/data/packageServer/3tzContent/README.md b/demos/data/packageServer/3tzContent/README.md
new file mode 100644
index 00000000..7393a1aa
--- /dev/null
+++ b/demos/data/packageServer/3tzContent/README.md
@@ -0,0 +1,4 @@
+
+This example is the same as `./specs/data/combineTilesets/nestedExternal`,
+but with the tilesets in `sub0` and `sub1` directories being converted
+into 3TZ archives.
diff --git a/demos/data/packageServer/3tzContent/externalA.json b/demos/data/packageServer/3tzContent/externalA.json
new file mode 100644
index 00000000..d4f878fb
--- /dev/null
+++ b/demos/data/packageServer/3tzContent/externalA.json
@@ -0,0 +1,31 @@
+{
+  "asset" : {
+    "version" : "1.1"
+  },
+  "geometricError" : 4.0,
+  "root" : {
+    "boundingVolume" : {
+      "box" : [ 0.5, -0.5, 0.5, 0.5, 0.0, 0.0, 0.0, 0.5, 0.0, 0.0, 0.0, 0.5 ]
+    },
+    "geometricError" : 2.0,
+    "children": [
+      {
+        "boundingVolume" : {
+          "box" : [ 0.5, -0.5, 0.5, 0.5, 0.0, 0.0, 0.0, 0.5, 0.0, 0.0, 0.0, 0.5 ]
+        },
+        "geometricError" : 1.0,
+        "content": {
+          "uri": "tileB.glb"
+        }
+      },  {
+        "boundingVolume" : {
+          "box" : [ 0.5, -0.5, 0.5, 0.5, 0.0, 0.0, 0.0, 0.5, 0.0, 0.0, 0.0, 0.5 ]
+        },
+        "geometricError" : 1.0,
+        "content": {
+          "uri": "sub1/externalC.3tz"
+        }
+      }      
+    ]
+  }
+}
\ No newline at end of file
diff --git a/demos/data/packageServer/3tzContent/sub0/externalB.3tz b/demos/data/packageServer/3tzContent/sub0/externalB.3tz
new file mode 100644
index 00000000..dae52c6e
Binary files /dev/null and b/demos/data/packageServer/3tzContent/sub0/externalB.3tz differ
diff --git a/demos/data/packageServer/3tzContent/sub1/externalC.3tz b/demos/data/packageServer/3tzContent/sub1/externalC.3tz
new file mode 100644
index 00000000..76d88141
Binary files /dev/null and b/demos/data/packageServer/3tzContent/sub1/externalC.3tz differ
diff --git a/demos/data/packageServer/3tzContent/tileA.glb b/demos/data/packageServer/3tzContent/tileA.glb
new file mode 100644
index 00000000..2602e2e2
Binary files /dev/null and b/demos/data/packageServer/3tzContent/tileA.glb differ
diff --git a/demos/data/packageServer/3tzContent/tileB.glb b/demos/data/packageServer/3tzContent/tileB.glb
new file mode 100644
index 00000000..2602e2e2
Binary files /dev/null and b/demos/data/packageServer/3tzContent/tileB.glb differ
diff --git a/demos/data/packageServer/3tzContent/tileset.json b/demos/data/packageServer/3tzContent/tileset.json
new file mode 100644
index 00000000..7e657b19
--- /dev/null
+++ b/demos/data/packageServer/3tzContent/tileset.json
@@ -0,0 +1,39 @@
+{
+  "asset" : {
+    "version" : "1.1"
+  },
+  "geometricError" : 4.0,
+  "root" : {
+    "boundingVolume" : {
+      "box" : [ 0.5, -0.5, 0.5, 0.5, 0.0, 0.0, 0.0, 0.5, 0.0, 0.0, 0.0, 0.5 ]
+    },
+    "geometricError" : 2.0,
+    "children": [
+      {
+        "boundingVolume" : {
+          "box" : [ 0.5, -0.5, 0.5, 0.5, 0.0, 0.0, 0.0, 0.5, 0.0, 0.0, 0.0, 0.5 ]
+        },
+        "geometricError" : 1.0,
+        "content": {
+          "uri": "tileA.glb"
+        }
+      }, {
+        "boundingVolume" : {
+          "box" : [ 0.5, -0.5, 0.5, 0.5, 0.0, 0.0, 0.0, 0.5, 0.0, 0.0, 0.0, 0.5 ]
+        },
+        "geometricError" : 1.0,
+        "content": {
+          "uri": "externalA.json"
+        }
+      },  {
+        "boundingVolume" : {
+          "box" : [ 0.5, -0.5, 0.5, 0.5, 0.0, 0.0, 0.0, 0.5, 0.0, 0.0, 0.0, 0.5 ]
+        },
+        "geometricError" : 1.0,
+        "content": {
+          "uri": "sub0/externalB.3tz"
+        }
+      }      
+    ]
+  }
+}
\ No newline at end of file
diff --git a/demos/packageServer/ContentDataTypeUtilities.ts b/demos/packageServer/ContentDataTypeUtilities.ts
new file mode 100644
index 00000000..ee36b854
--- /dev/null
+++ b/demos/packageServer/ContentDataTypeUtilities.ts
@@ -0,0 +1,111 @@
+import { ContentDataTypes } from "../../src/contentTypes/ContentDataTypes";
+
+/**
+ * Utility methods for determining default file extensions and MIME
+ * types for a `ContentDataType`.
+ *
+ * These are only used in the package server demo. The functionality
+ * could later become part of the `contentTypes` package, maybe as
+ * part of the `ContentDataTypeRegistry`.
+ *
+ * @internal
+ */
+export class ContentDataTypeUtilities {
+  /**
+   * A mapping from `ContentDataType` strings to "default" file
+   * extensions (without the `.` dot)
+   */
+  private static extensions: { [key: string]: string };
+
+  /**
+   * A mapping from `ContentDataType` strings to MIME types
+   */
+  private static mimeTypes: { [key: string]: string };
+
+  /**
+   * Initialize the `extensions` dictionary if it was not
+   * initialized yet.
+   */
+  private static initializeExtensions() {
+    if (ContentDataTypeUtilities.extensions !== undefined) {
+      return;
+    }
+    const d: { [key: string]: string } = {};
+    d[ContentDataTypes.CONTENT_TYPE_GLB] = "glb";
+    d[ContentDataTypes.CONTENT_TYPE_B3DM] = "b3dm";
+    d[ContentDataTypes.CONTENT_TYPE_I3DM] = "i3dm";
+    d[ContentDataTypes.CONTENT_TYPE_CMPT] = "cmpt";
+    d[ContentDataTypes.CONTENT_TYPE_PNTS] = "pnts";
+    d[ContentDataTypes.CONTENT_TYPE_GEOM] = "geom";
+    d[ContentDataTypes.CONTENT_TYPE_VCTR] = "vctr";
+    d[ContentDataTypes.CONTENT_TYPE_SUBT] = "subtree";
+    d[ContentDataTypes.CONTENT_TYPE_PNG] = "png";
+    d[ContentDataTypes.CONTENT_TYPE_JPEG] = "jpg";
+    d[ContentDataTypes.CONTENT_TYPE_GIF] = "gif";
+    d[ContentDataTypes.CONTENT_TYPE_GEOJSON] = "geojson";
+    d[ContentDataTypes.CONTENT_TYPE_3TZ] = "3tz";
+    d[ContentDataTypes.CONTENT_TYPE_GLTF] = "gltf";
+    d[ContentDataTypes.CONTENT_TYPE_TILESET] = "json";
+    ContentDataTypeUtilities.extensions = d;
+  }
+
+  /**
+   * Initialize the `mimeTypes` dictionary if it was not
+   * initialized yet.
+   */
+  private static initializeMimeTypes() {
+    if (ContentDataTypeUtilities.mimeTypes !== undefined) {
+      return;
+    }
+    const d: { [key: string]: string } = {};
+    d[ContentDataTypes.CONTENT_TYPE_GLB] = "model/gltf-binary";
+    d[ContentDataTypes.CONTENT_TYPE_B3DM] = "application/octet-stream";
+    d[ContentDataTypes.CONTENT_TYPE_I3DM] = "application/octet-stream";
+    d[ContentDataTypes.CONTENT_TYPE_CMPT] = "application/octet-stream";
+    d[ContentDataTypes.CONTENT_TYPE_PNTS] = "application/octet-stream";
+    d[ContentDataTypes.CONTENT_TYPE_GEOM] = "text/plain"; // ???
+    d[ContentDataTypes.CONTENT_TYPE_VCTR] = "application/json"; // ???
+    d[ContentDataTypes.CONTENT_TYPE_SUBT] = "application/octet-stream";
+    d[ContentDataTypes.CONTENT_TYPE_PNG] = "image/png";
+    d[ContentDataTypes.CONTENT_TYPE_JPEG] = "image/jpeg";
+    d[ContentDataTypes.CONTENT_TYPE_GIF] = "image/gif";
+    d[ContentDataTypes.CONTENT_TYPE_GEOJSON] = "application/json"; // ???
+    d[ContentDataTypes.CONTENT_TYPE_3TZ] = "application/octet-stream"; // ???
+    d[ContentDataTypes.CONTENT_TYPE_GLTF] = "model/gltf+json";
+    d[ContentDataTypes.CONTENT_TYPE_TILESET] = "application/json";
+    ContentDataTypeUtilities.mimeTypes = d;
+  }
+
+  /**
+   * Returns the "default" file extension (without `.` dot) for the
+   * given content data type, or `undefined` if the given type is
+   * `undefined` or not known.
+   *
+   * @param contentDataType The `ContentDataType` string
+   * @returns The file extension, without `.` dot
+   */
+  static getFileExtension(
+    contentDataType: string | undefined
+  ): string | undefined {
+    if (contentDataType === undefined) {
+      return undefined;
+    }
+    ContentDataTypeUtilities.initializeExtensions();
+    return ContentDataTypeUtilities.extensions[contentDataType];
+  }
+
+  /**
+   * Returns the MIME type for the given content data type, or
+   * `undefined` if the given type is `undefined` or not known.
+   *
+   * @param contentDataType The `ContentDataType` string
+   * @returns The file extension, without `.` dot
+   */
+  static getMimeType(contentDataType: string | undefined): string | undefined {
+    if (contentDataType === undefined) {
+      return undefined;
+    }
+    ContentDataTypeUtilities.initializeMimeTypes();
+    return ContentDataTypeUtilities.mimeTypes[contentDataType];
+  }
+}
diff --git a/demos/packageServer/PackageServer.ts b/demos/packageServer/PackageServer.ts
new file mode 100644
index 00000000..97aca84f
--- /dev/null
+++ b/demos/packageServer/PackageServer.ts
@@ -0,0 +1,266 @@
+import path from "path";
+import http from "http";
+
+import { Buffers } from "../../src/base/Buffers";
+import { Paths } from "../../src/base/Paths";
+
+import { TilesetSource } from "../../src/tilesetData/TilesetSource";
+import { TilesetSources } from "../../src/tilesetData/TilesetSources";
+
+import { ContentDataTypes } from "../../src/contentTypes/ContentDataTypes";
+import { ContentDataTypeRegistry } from "../../src/contentTypes/ContentDataTypeRegistry";
+
+import { ContentDataTypeUtilities } from "./ContentDataTypeUtilities";
+
+import { Loggers } from "../../src/logging/Loggers";
+import { PackageServerOptions } from "./PackageServerOptions";
+
+const logger = Loggers.get("packageServer");
+
+export class PackageServer {
+  /**
+   * The base directory from which the server is serving.
+   *
+   * This is used for resolving the content from the
+   * root tileset source (if it was a tileset JSON file)
+   */
+  private readonly baseDirectory: string;
+
+  /**
+   * The tileset sources that the server is serving from.
+   *
+   * The key of each entry is the name of the tileset source
+   * relative to the base directory. The key for the "root"
+   * tileset source is `""` (the empty string).
+   *
+   * For example, when a tileset refers to `data/external.3tz`,
+   * then the entry with the key `data/external.3tz` will
+   * contain the data of the external 3TZ package.
+   */
+  private tilesetSources: { [key: string]: TilesetSource } = {};
+
+  /**
+   * Creates a new instance
+   *
+   * @param baseDirectory - The base directory
+   */
+  constructor(baseDirectory: string) {
+    this.baseDirectory = baseDirectory;
+  }
+
+  /**
+   * Start the server based on the given options
+   *
+   * @param options The options
+   */
+  start(options: PackageServerOptions) {
+    const hostName = options.hostName;
+    const port = options.port;
+    const sourceName = options.sourceName;
+
+    const tilesetSource = TilesetSources.createAndOpen(sourceName);
+    if (!tilesetSource) {
+      logger.error("Could not create source for " + sourceName);
+      return;
+    }
+    this.tilesetSources[""] = tilesetSource;
+
+    const server = http.createServer((req, res) =>
+      this.handleRequest(req, res)
+    );
+    server.listen(port, hostName, () => {
+      logger.info(`Server running at http://${hostName}:${port}/`);
+    });
+  }
+
+  /**
+   * Set overly permissive CORS header options for local tests
+   *
+   * @param res - The server response
+   */
+  private static setCorsHeader(res: http.ServerResponse<http.IncomingMessage>) {
+    res.setHeader("Access-Control-Allow-Origin", "*");
+    res.setHeader("Access-Control-Request-Method", "*");
+    res.setHeader("Access-Control-Allow-Methods", "OPTIONS, GET");
+    res.setHeader(
+      "Access-Control-Allow-Headers",
+      "Origin, X-Requested-With, Content-Type, Accept"
+    );
+  }
+
+  /**
+   * The request handler for the node http server
+   *
+   * @param req The request
+   * @param res The response
+   */
+  private async handleRequest(
+    req: http.IncomingMessage,
+    res: http.ServerResponse<http.IncomingMessage>
+  ): Promise<void> {
+    if (!req.url) {
+      logger.warn("Return 404 for undefined URL");
+      res.statusCode = 404;
+      res.end();
+      return;
+    }
+
+    PackageServer.setCorsHeader(res);
+    if (req.method === "OPTIONS") {
+      res.setHeader("Allow", "OPTIONS, GET");
+      res.writeHead(204);
+      res.end();
+      return;
+    }
+
+    // TODO Anything to be done for HTTPS here?
+    // (We only use the `pathname` anyhow, so probably not...)
+    const url = new URL(`http://${req.headers.host}${req.url}`);
+    //console.log("url ", url);
+    await this.handleResponseForUrlPathname(res, url.pathname);
+  }
+
+  /**
+   * Resolve the content data for the given key.
+   *
+   * The key is just the URL pathname, without a leading slash,
+   * used for looking up entries in packages.
+   *
+   * This will try to look up the key in all known tileset sources,
+   * and return the first content that is found for this key.
+   *
+   * @param key - The key
+   * @returns - The content data
+   */
+  private resolveContentData(key: string): Buffer | undefined {
+    logger.info(`Resolve content data for key ${key}`);
+
+    for (const name of Object.keys(this.tilesetSources)) {
+      const tilesetSource = this.tilesetSources[name];
+
+      const dirName = path.dirname(name);
+      const relatviveKey = Paths.relativize(dirName, key);
+
+      logger.info(`  Looking up ${relatviveKey} in source "${name}"`);
+      const content = tilesetSource.getValue(relatviveKey);
+      if (content) {
+        logger.info(
+          `  Looking up ${relatviveKey} in source "${name}" succeeded`
+        );
+        return content;
+      }
+      logger.info(`  Looking up ${relatviveKey} in source "${name}" failed`);
+    }
+
+    logger.info(`Resolve content data for key ${key} FAILED!`);
+    return undefined;
+  }
+
+  /**
+   * Returns the data of the top-level tileset JSON from the package
+   * that is identified with the given key.
+   *
+   * If the respective package has not been opened yet, then it
+   * will be opened and stored as one of the `this.tilesetSources`.
+   *
+   * @param key - The key
+   * @returns The tileset JSON data
+   */
+  private resolvePackageTilesetData(key: string): Buffer | undefined {
+    logger.info(`Resolve tileset data for package key ${key}`);
+
+    let tilesetSource = this.tilesetSources[key];
+    if (!tilesetSource) {
+      const fullSourceName = path.resolve(this.baseDirectory, key);
+      try {
+        tilesetSource = TilesetSources.createAndOpen(fullSourceName);
+      } catch (error) {
+        logger.error(
+          `Could not open tileset source for key ${key} with full source name ${fullSourceName}`
+        );
+        return undefined;
+      }
+      this.tilesetSources[key] = tilesetSource;
+    }
+    const content = tilesetSource.getValue("tileset.json");
+    if (content) {
+      logger.info(`Resolve tileset data for package key ${key} succeeded`);
+      return content;
+    }
+    logger.info(`Resolve tileset data for package key ${key} failed`);
+    return undefined;
+  }
+
+  /**
+   * Handle the response for the given URL pathname.
+   *
+   * This will try to look up the data that is identified with the
+   * given path name, and send it out via the given response.
+   *
+   * If the given path name refers to a package (3TZ file), then
+   * this package will be opened internally and used for serving
+   * subsequent requests, with the first response being the
+   * top-level "tileset.json" data from this package.
+   *
+   * @param res - The response
+   * @param urlPathname - The URL pathname
+   */
+  private async handleResponseForUrlPathname(
+    res: http.ServerResponse<http.IncomingMessage>,
+    urlPathname: string
+  ): Promise<void> {
+    logger.info(`Handle response for URL pathname ${urlPathname}`);
+
+    const key = urlPathname.startsWith("/")
+      ? urlPathname.substring(1)
+      : urlPathname;
+
+    // Try to resolve the content data
+    let content = this.resolveContentData(key);
+    if (!content) {
+      logger.info(`Return 404 for URL pathname ${urlPathname}`);
+      res.statusCode = 404;
+      res.end();
+      return;
+    }
+
+    // If the content is a 3TZ package, then the content data
+    // will be its top-level tileset JSON
+    let contentDataType = await ContentDataTypeRegistry.findType(key, content);
+    if (contentDataType === ContentDataTypes.CONTENT_TYPE_3TZ) {
+      logger.info(`Found 3TZ content for key ${key}`);
+      content = this.resolvePackageTilesetData(key);
+      if (!content) {
+        logger.info(`Return 404 for URL pathname ${urlPathname}`);
+        res.statusCode = 404;
+        res.end();
+        return;
+      }
+      // Assuming that the "tileset.json" is actually a tileset JSON:
+      contentDataType = ContentDataTypes.CONTENT_TYPE_TILESET;
+    }
+
+    // Prepare the headers for the response
+    let mimeType = ContentDataTypeUtilities.getMimeType(contentDataType);
+    if (mimeType === undefined) {
+      mimeType = "application/octet-stream";
+    }
+    const headers: http.OutgoingHttpHeaders = {
+      "Content-Type": mimeType,
+      "Content-Length": content.length,
+    };
+    if (Buffers.isGzipped(content)) {
+      headers["Content-Encoding"] = "gzip";
+    }
+
+    // Send out the actual resonse
+    logger.info(`Handle response for URL pathname ${urlPathname} succeeded:`);
+    logger.info(`  key: ${key}`);
+    logger.info(`  mimeType: ${mimeType}`);
+    logger.info(`  content.length: ${content.length}`);
+
+    res.writeHead(200, headers);
+    res.end(content);
+    return;
+  }
+}
diff --git a/demos/packageServer/PackageServerOptions.ts b/demos/packageServer/PackageServerOptions.ts
new file mode 100644
index 00000000..67e45d1e
--- /dev/null
+++ b/demos/packageServer/PackageServerOptions.ts
@@ -0,0 +1,20 @@
+/**
+ * Options for starting the package server
+ */
+export type PackageServerOptions = {
+  /**
+   * The host name
+   */
+  hostName: string;
+
+  /**
+   * The port
+   */
+  port: number;
+
+  /**
+   * The full name of the (root) tileset source that
+   * should be served.
+   */
+  sourceName: string;
+};
diff --git a/demos/packageServer/packageServerMain.ts b/demos/packageServer/packageServerMain.ts
new file mode 100644
index 00000000..cefeacf6
--- /dev/null
+++ b/demos/packageServer/packageServerMain.ts
@@ -0,0 +1,90 @@
+import path from "path";
+import minimist from "minimist";
+
+import { Paths } from "../../src/base/Paths";
+import { defined } from "../../src/base/defined";
+import { defaultValue } from "../../src/base/defaultValue";
+
+import { PackageServer } from "./PackageServer";
+
+import { Loggers } from "../../src/logging/Loggers";
+import { PackageServerOptions } from "./PackageServerOptions";
+
+const logger = Loggers.get("packageServer");
+
+/**
+ * Print the help message showing the command line options
+ */
+function printHelp() {
+  const help =
+    "Usage: PackageServer [OPTIONS]\n" +
+    "  -n,  --hostName <name>     Host name. Default: '127.0.0.1' (localhost).\n" +
+    "  -p,  --port <number>       Port number. Default: '8003'.\n" +
+    "  -s,  --sourceName <name>   Package file or directory name.\n" +
+    "  -h   --help                Print help. Not more than what you're currently seeing.\n";
+  console.log(help);
+}
+
+/**
+ * Parses the options from the command line arguments.
+ *
+ * If the 'help' should be printed, or the arguments cannot be parsed,
+ * then the help is printed and `undefined` is returned.
+ *
+ * @param {minimist.ParsedArgs} args The arguments
+ * @returns The options
+ */
+function parseOptions(args: any) {
+  if (defined(args.h) || defined(args.help)) {
+    printHelp();
+    return undefined;
+  }
+
+  const hostName = defaultValue(
+    defaultValue(args.n, args.hostName),
+    "127.0.0.1"
+  );
+  const port = defaultValue(defaultValue(args.p, args.port), "8003");
+  let sourceName = "";
+  sourceName = defaultValue(args.s, args.sourceName);
+
+  if (!defined(sourceName)) {
+    logger.warn("No source name was given");
+    printHelp();
+    return undefined;
+  }
+
+  const options = {
+    hostName: hostName,
+    port: port,
+    sourceName: sourceName,
+  };
+  return options;
+}
+
+/**
+ * Run the package server
+ */
+async function run() {
+  const parsedArguments = minimist(process.argv.slice(2));
+  const options = parseOptions(parsedArguments);
+  if (!defined(options)) {
+    return;
+  }
+
+  const sourceName = options.sourceName;
+  let baseDirectory = sourceName;
+  if (!Paths.isDirectory(sourceName)) {
+    baseDirectory = path.dirname(sourceName);
+  }
+
+  const packageServer = new PackageServer(baseDirectory);
+  const serverOptions: PackageServerOptions = {
+    hostName: options.hostName,
+    port: options.port,
+    sourceName: options.sourceName,
+  };
+  packageServer.start(serverOptions);
+}
+
+run();
diff --git a/specs/data/combineTilesets/nestedExternal/README.md b/specs/data/combineTilesets/nestedExternal/README.md
index 32a949f2..b864dc6d 100644
--- a/specs/data/combineTilesets/nestedExternal/README.md
+++ b/specs/data/combineTilesets/nestedExternal/README.md
@@ -1,20 +1,20 @@
 ```
 tileset.json refers to
-  tileA.b3dm
+  tileA.glb
   externalA.json
   sub0/externalB.json
   
 externalA.json refers to
-  tileB.b3dm
+  tileB.glb
   sub1/externalC.json
   
 sub0/externalB.json refers to
-  tileC.b3dm
-  sub01/tileD.b3dm
+  tileC.glb
+  sub01/tileD.glb
 
 sub1/externalC.json refers to
-  tileE.b3dm
-  sub10/tileF.b3dm
+  tileE.glb
+  sub10/tileF.glb
 ```  
   
   
diff --git a/specs/data/combineTilesets/nestedExternal/externalA.json b/specs/data/combineTilesets/nestedExternal/externalA.json
index 98ff8810..a3f4c346 100644
--- a/specs/data/combineTilesets/nestedExternal/externalA.json
+++ b/specs/data/combineTilesets/nestedExternal/externalA.json
@@ -1,31 +1,31 @@
 {
-    "asset" : {
-      "version" : "1.1"
+  "asset" : {
+    "version" : "1.1"
+  },
+  "geometricError" : 4.0,
+  "root" : {
+    "boundingVolume" : {
+      "box" : [ 0.5, -0.5, 0.5, 0.5, 0.0, 0.0, 0.0, 0.5, 0.0, 0.0, 0.0, 0.5 ]
     },
-    "geometricError" : 4.0,
-    "root" : {
-      "boundingVolume" : {
-        "box" : [ 0.5, 0.5, 0.5, 0.5, 0.0, 0.0, 0.0, 0.5, 0.0, 0.0, 0.0, 0.5 ]
-      },
-      "geometricError" : 2.0,
-      "children": [
-        {
-          "boundingVolume" : {
-            "box" : [ 0.5, 0.5, 0.5, 0.5, 0.0, 0.0, 0.0, 0.5, 0.0, 0.0, 0.0, 0.5 ]
-          },
-          "geometricError" : 1.0,
-          "content": {
-            "uri": "tileB.b3dm"
-          }
-        },  {
-          "boundingVolume" : {
-            "box" : [ 0.5, 0.5, 0.5, 0.5, 0.0, 0.0, 0.0, 0.5, 0.0, 0.0, 0.0, 0.5 ]
-          },
-          "geometricError" : 1.0,
-          "content": {
-            "uri": "sub1/externalC.json"
-          }
-        }      
-      ]
-    }
-  }
\ No newline at end of file
+    "geometricError" : 2.0,
+    "children": [
+      {
+        "boundingVolume" : {
+          "box" : [ 0.5, -0.5, 0.5, 0.5, 0.0, 0.0, 0.0, 0.5, 0.0, 0.0, 0.0, 0.5 ]
+        },
+        "geometricError" : 1.0,
+        "content": {
+          "uri": "tileB.glb"
+        }
+      },  {
+        "boundingVolume" : {
+          "box" : [ 0.5, -0.5, 0.5, 0.5, 0.0, 0.0, 0.0, 0.5, 0.0, 0.0, 0.0, 0.5 ]
+        },
+        "geometricError" : 1.0,
+        "content": {
+          "uri": "sub1/externalC.json"
+        }
+      }      
+    ]
+  }
+}
\ No newline at end of file
diff --git a/specs/data/combineTilesets/nestedExternal/sub0/externalB.json b/specs/data/combineTilesets/nestedExternal/sub0/externalB.json
index ea1939b9..54f4d0bc 100644
--- a/specs/data/combineTilesets/nestedExternal/sub0/externalB.json
+++ b/specs/data/combineTilesets/nestedExternal/sub0/externalB.json
@@ -5,25 +5,25 @@
   "geometricError" : 4.0,
   "root" : {
     "boundingVolume" : {
-      "box" : [ 0.5, 0.5, 0.5, 0.5, 0.0, 0.0, 0.0, 0.5, 0.0, 0.0, 0.0, 0.5 ]
+      "box" : [ 0.5, -0.5, 0.5, 0.5, 0.0, 0.0, 0.0, 0.5, 0.0, 0.0, 0.0, 0.5 ]
     },
     "geometricError" : 2.0,
     "children": [
       {
         "boundingVolume" : {
-          "box" : [ 0.5, 0.5, 0.5, 0.5, 0.0, 0.0, 0.0, 0.5, 0.0, 0.0, 0.0, 0.5 ]
+          "box" : [ 0.5, -0.5, 0.5, 0.5, 0.0, 0.0, 0.0, 0.5, 0.0, 0.0, 0.0, 0.5 ]
         },
         "geometricError" : 1.0,
         "content": {
-          "uri": "tileC.b3dm"
+          "uri": "tileC.glb"
         }
       },  {
         "boundingVolume" : {
-          "box" : [ 0.5, 0.5, 0.5, 0.5, 0.0, 0.0, 0.0, 0.5, 0.0, 0.0, 0.0, 0.5 ]
+          "box" : [ 0.5, -0.5, 0.5, 0.5, 0.0, 0.0, 0.0, 0.5, 0.0, 0.0, 0.0, 0.5 ]
         },
         "geometricError" : 1.0,
         "content": {
-          "uri": "sub01/tileD.b3dm"
+          "uri": "sub01/tileD.glb"
         }
       }      
     ]
diff --git a/specs/data/combineTilesets/nestedExternal/sub0/sub01/tileD.b3dm b/specs/data/combineTilesets/nestedExternal/sub0/sub01/tileD.b3dm
deleted file mode 100644
index e69de29b..00000000
diff --git a/specs/data/combineTilesets/nestedExternal/sub0/sub01/tileD.glb b/specs/data/combineTilesets/nestedExternal/sub0/sub01/tileD.glb
new file mode 100644
index 00000000..2602e2e2
Binary files /dev/null and b/specs/data/combineTilesets/nestedExternal/sub0/sub01/tileD.glb differ
diff --git a/specs/data/combineTilesets/nestedExternal/sub0/tileC.b3dm b/specs/data/combineTilesets/nestedExternal/sub0/tileC.b3dm
deleted file mode 100644
index e69de29b..00000000
diff --git a/specs/data/combineTilesets/nestedExternal/sub0/tileC.glb b/specs/data/combineTilesets/nestedExternal/sub0/tileC.glb
new file mode 100644
index 00000000..2602e2e2
Binary files /dev/null and b/specs/data/combineTilesets/nestedExternal/sub0/tileC.glb differ
diff --git a/specs/data/combineTilesets/nestedExternal/sub1/externalC.json b/specs/data/combineTilesets/nestedExternal/sub1/externalC.json
index 02c71b20..7139d1f0 100644
--- a/specs/data/combineTilesets/nestedExternal/sub1/externalC.json
+++ b/specs/data/combineTilesets/nestedExternal/sub1/externalC.json
@@ -5,25 +5,25 @@
   "geometricError" : 4.0,
   "root" : {
     "boundingVolume" : {
-      "box" : [ 0.5, 0.5, 0.5, 0.5, 0.0, 0.0, 0.0, 0.5, 0.0, 0.0, 0.0, 0.5 ]
+      "box" : [ 0.5, -0.5, 0.5, 0.5, 0.0, 0.0, 0.0, 0.5, 0.0, 0.0, 0.0, 0.5 ]
     },
     "geometricError" : 2.0,
     "children": [
       {
         "boundingVolume" : {
-          "box" : [ 0.5, 0.5, 0.5, 0.5, 0.0, 0.0, 0.0, 0.5, 0.0, 0.0, 0.0, 0.5 ]
+          "box" : [ 0.5, -0.5, 0.5, 0.5, 0.0, 0.0, 0.0, 0.5, 0.0, 0.0, 0.0, 0.5 ]
         },
         "geometricError" : 1.0,
         "content": {
-          "uri": "tileE.b3dm"
+          "uri": "tileE.glb"
         }
       },  {
         "boundingVolume" : {
-          "box" : [ 0.5, 0.5, 0.5, 0.5, 0.0, 0.0, 0.0, 0.5, 0.0, 0.0, 0.0, 0.5 ]
+          "box" : [ 0.5, -0.5, 0.5, 0.5, 0.0, 0.0, 0.0, 0.5, 0.0, 0.0, 0.0, 0.5 ]
         },
         "geometricError" : 1.0,
         "content": {
-          "uri": "sub10/tileF.b3dm"
+          "uri": "sub10/tileF.glb"
         }
       }      
     ]
diff --git a/specs/data/combineTilesets/nestedExternal/sub1/sub10/tileF.b3dm b/specs/data/combineTilesets/nestedExternal/sub1/sub10/tileF.b3dm
deleted file mode 100644
index e69de29b..00000000
diff --git a/specs/data/combineTilesets/nestedExternal/sub1/sub10/tileF.glb b/specs/data/combineTilesets/nestedExternal/sub1/sub10/tileF.glb
new file mode 100644
index 00000000..2602e2e2
Binary files /dev/null and b/specs/data/combineTilesets/nestedExternal/sub1/sub10/tileF.glb differ
diff --git a/specs/data/combineTilesets/nestedExternal/sub1/tileE.b3dm b/specs/data/combineTilesets/nestedExternal/sub1/tileE.b3dm
deleted file mode 100644
index e69de29b..00000000
diff --git a/specs/data/combineTilesets/nestedExternal/sub1/tileE.glb b/specs/data/combineTilesets/nestedExternal/sub1/tileE.glb
new file mode 100644
index 00000000..2602e2e2
Binary files /dev/null and b/specs/data/combineTilesets/nestedExternal/sub1/tileE.glb differ
diff --git a/specs/data/combineTilesets/nestedExternal/tileA.b3dm b/specs/data/combineTilesets/nestedExternal/tileA.b3dm
deleted file mode 100644
index e69de29b..00000000
diff --git a/specs/data/combineTilesets/nestedExternal/tileA.glb b/specs/data/combineTilesets/nestedExternal/tileA.glb
new file mode 100644
index 00000000..2602e2e2
Binary files /dev/null and b/specs/data/combineTilesets/nestedExternal/tileA.glb differ
diff --git a/specs/data/combineTilesets/nestedExternal/tileB.b3dm b/specs/data/combineTilesets/nestedExternal/tileB.b3dm
deleted file mode 100644
index e69de29b..00000000
diff --git a/specs/data/combineTilesets/nestedExternal/tileB.glb b/specs/data/combineTilesets/nestedExternal/tileB.glb
new file mode 100644
index 00000000..2602e2e2
Binary files /dev/null and b/specs/data/combineTilesets/nestedExternal/tileB.glb differ
diff --git a/specs/data/combineTilesets/nestedExternal/tileset.json b/specs/data/combineTilesets/nestedExternal/tileset.json
index 078c879d..b1e1c92c 100644
--- a/specs/data/combineTilesets/nestedExternal/tileset.json
+++ b/specs/data/combineTilesets/nestedExternal/tileset.json
@@ -5,21 +5,21 @@
   "geometricError" : 4.0,
   "root" : {
     "boundingVolume" : {
-      "box" : [ 0.5, 0.5, 0.5, 0.5, 0.0, 0.0, 0.0, 0.5, 0.0, 0.0, 0.0, 0.5 ]
+      "box" : [ 0.5, -0.5, 0.5, 0.5, 0.0, 0.0, 0.0, 0.5, 0.0, 0.0, 0.0, 0.5 ]
     },
     "geometricError" : 2.0,
     "children": [
       {
         "boundingVolume" : {
-          "box" : [ 0.5, 0.5, 0.5, 0.5, 0.0, 0.0, 0.0, 0.5, 0.0, 0.0, 0.0, 0.5 ]
+          "box" : [ 0.5, -0.5, 0.5, 0.5, 0.0, 0.0, 0.0, 0.5, 0.0, 0.0, 0.0, 0.5 ]
         },
         "geometricError" : 1.0,
         "content": {
-          "uri": "tileA.b3dm"
+          "uri": "tileA.glb"
         }
       }, {
         "boundingVolume" : {
-          "box" : [ 0.5, 0.5, 0.5, 0.5, 0.0, 0.0, 0.0, 0.5, 0.0, 0.0, 0.0, 0.5 ]
+          "box" : [ 0.5, -0.5, 0.5, 0.5, 0.0, 0.0, 0.0, 0.5, 0.0, 0.0, 0.0, 0.5 ]
         },
         "geometricError" : 1.0,
         "content": {
@@ -27,7 +27,7 @@
         }
       },  {
         "boundingVolume" : {
-          "box" : [ 0.5, 0.5, 0.5, 0.5, 0.0, 0.0, 0.0, 0.5, 0.0, 0.0, 0.0, 0.5 ]
+          "box" : [ 0.5, -0.5, 0.5, 0.5, 0.0, 0.0, 0.0, 0.5, 0.0, 0.0, 0.0, 0.5 ]
         },
         "geometricError" : 1.0,
         "content": {