---
name: obj-exporter
description: Three.js OBJExporter utility for exporting 3D geometry to Wavefront OBJ format. Use when converting Three.js scenes, meshes, or geometries to OBJ files for use in other 3D software like Blender, Maya, or MeshLab.
---

# OBJExporter Guide

## Basic Structure

OBJ is a text-based 3D geometry format:

```
# Comment
v x y z        # Vertex position
vn x y z       # Vertex normal
f v1 v2 v3     # Face (triangle)
f v1/vt1/vn1 v2/vt2/vn2 v3/vt3/vn3  # Face with texture/normal indices
```

Example:
```
# Cube
v 0 0 0
v 1 0 0
v 1 1 0
v 0 1 0
f 1 2 3
f 1 3 4
```

## Three.js OBJExporter

Three.js provides `OBJExporter` in examples:

```javascript
import { OBJExporter } from 'three/examples/jsm/exporters/OBJExporter.js';

const exporter = new OBJExporter();
const objString = exporter.parse(object3D);

// Write to file (Node.js)
import fs from 'fs';
fs.writeFileSync('output.obj', objString);
```

## Exporting with World Transforms

To export geometry in world coordinates:

```javascript
// Update world matrices first
root.updateMatrixWorld(true);

// Clone and transform geometry
const worldGeometry = mesh.geometry.clone();
worldGeometry.applyMatrix4(mesh.matrixWorld);

// Create new mesh for export
const exportMesh = new THREE.Mesh(worldGeometry);
const objData = exporter.parse(exportMesh);
```

## Merging Multiple Geometries

```javascript
import { mergeGeometries } from 'three/examples/jsm/utils/BufferGeometryUtils.js';

const geometries = [];
root.traverse((obj) => {
  if (obj instanceof THREE.Mesh) {
    const geom = obj.geometry.clone();
    geom.applyMatrix4(obj.matrixWorld);
    geometries.push(geom);
  }
});

const merged = mergeGeometries(geometries);
const mergedMesh = new THREE.Mesh(merged);
const objData = exporter.parse(mergedMesh);
```

## Node.js ES Module Setup

For running Three.js in Node.js:

```json
// package.json
{ "type": "module" }
```

```javascript
// script.js
import * as THREE from 'three';
import { OBJExporter } from 'three/examples/jsm/exporters/OBJExporter.js';
```