BabylonJS/Babylon.js · error · Error

Unable to deserialize NavMesh.

Error message

Unable to deserialize NavMesh.

What it means

BuildFromNavmeshData deserializes a previously saved navmesh by passing the raw bytes to Recast's importNavMesh. It throws when the import returns no navMesh object, meaning the WASM library could not parse the data — the bytes are corrupt, truncated, or were produced by an incompatible Recast version/build.

Source

Thrown at packages/dev/addons/src/navigation/generator/generator.common.ts:18

import { type TileCacheMeshProcess } from "@recast-navigation/core";

import { GetRecast } from "../factory/common";

/**
 *  Builds a NavMesh and NavMeshQuery from serialized data.
 *  @param data The serialized NavMesh data.
 *  @returns An object containing the NavMesh and NavMeshQuery.
 *  @remarks This function deserializes the NavMesh data and creates a NavMeshQuery
 *  instance for querying the NavMesh.
 *  @throws Error if the NavMesh data is invalid or cannot be deserialized.
 */
export function BuildFromNavmeshData(data: Uint8Array) {
    const recast = GetRecast();
    const result = recast.importNavMesh(data);

    if (!result.navMesh) {
        throw new Error(`Unable to deserialize NavMesh.`);
    }

    return {
        navMesh: result.navMesh,
        navMeshQuery: new recast.NavMeshQuery(result.navMesh),
        tileCache: undefined,
    };
}

/**
 * Builds a TileCache and NavMeshQuery from serialized data.
 * @param data The serialized TileCache data.
 * @param tileCacheMeshProcess Optional function to process the TileCache mesh.
 * @returns An object containing the TileCache, NavMesh, and NavMeshQuery.
 */
export function BuildFromTileCacheData(data: Uint8Array, tileCacheMeshProcess: TileCacheMeshProcess) {
    const recast = GetRecast();
    const result = recast.importTileCache(data, tileCacheMeshProcess);

View on GitHub (pinned to 0592b347b8)

Solutions

1. Verify the data source: log/check `data.byteLength` and confirm the fetch returned the expected binary asset, not an error page.
2. Re-export/save the navmesh with the same recast-navigation-js version that is initialized at runtime.
3. Wrap the call in try/catch and fall back to rebuilding (generating) the navmesh from source geometry when deserialization fails.

Example fix

// before
const data = new Uint8Array(await (await fetch("navmesh.bin")).arrayBuffer());
const nav = BuildFromNavmeshData(data); // may throw on corrupt data
// after
const res = await fetch("navmesh.bin");
if (!res.ok) throw new Error("navmesh download failed");
const data = new Uint8Array(await res.arrayBuffer());
const nav = BuildFromNavmeshData(data); // only called with verified bytes

const res = await fetch(navmeshUrl);
if (!res.ok) throw new Error(`navmesh fetch failed: ${res.status}`);
const buf = await res.arrayBuffer();
if (buf.byteLength === 0) throw new Error("navmesh data empty");
const nav = BuildFromNavmeshData(new Uint8Array(buf));

const isPlausibleNavmeshData = (d: Uint8Array): boolean => d.byteLength > 0 && d.byteLength % 4 === 0;

try {
  nav = BuildFromNavmeshData(data);
} catch (e) {
  if (String(e).includes("Unable to deserialize NavMesh")) {
    nav = generateNavmeshFromSceneGeometry(); // rebuild fallback
  } else throw e;
}

When it happens

Trigger: Calling BuildFromNavmeshData(data) with a Uint8Array that is not a valid serialized navmesh: empty/garbage data, a file corrupted in transfer, or data serialized by a different recast-navigation-js version than the one initialized.

Common situations: Loading a saved .navmesh/.bin asset fetched over the network (404 HTML page or truncated download), version mismatch after upgrading the Recast WASM package, or passing tileCache data to the navmesh importer by mistake.

Related errors

• Unable to deserialize TileCache.
• Recast is not initialized. Please call InitRecast first.
• Unable to generateSoloNavMesh: ${result.error}
• At least one mesh is needed to create the nav mesh.
• Unable to get nav mesh. No vertices or indices.

AI-assisted analysis of BabylonJS/Babylon.js@0592b347b8 (2026-08-30). Data as JSON: /api/errors/c059adc14c7868ff. Report an issue: GitHub.