I've asked this and got the answer:

```
var geom = new THREE.Geometry();
var v1 = new THREE.Vector3(0,0,0);
var v2 = new THREE.Vector3(0,500,0);
var v3 = new THREE.Vector3(0,500,500);
geom.vertices.push(new THREE.Vertex(v1));
geom.vertices.push(new THREE.Vertex(v2));
geom.vertices.push(new THREE.Vertex(v3));
var object = new THREE.Mesh( geom, new THREE.MeshNormalMaterial() );
scene.addObject(object);
```

I expected this to work but it didn't.

You've added vertices, but forgot to put those vertices into a face and add that to the geometry:

```
geom.faces.push( new THREE.Face3( 0, 1, 2 ) );
```

so your snippet becomes:

```
var geom = new THREE.Geometry();
var v1 = new THREE.Vector3(0,0,0);
var v2 = new THREE.Vector3(0,500,0);
var v3 = new THREE.Vector3(0,500,500);
geom.vertices.push(v1);
geom.vertices.push(v2);
geom.vertices.push(v3);
geom.faces.push( new THREE.Face3( 0, 1, 2 ) );
var object = new THREE.Mesh( geom, new THREE.MeshNormalMaterial() );
scene.addObject(object);
```

The idea is that a Face3 instance references 3 vertices(the x,y,z coords you've added previously to the geometry) by using the indices of the vertices in the list/array. Currently you only have 3 vertices and you want to connect them,so your face references index 0,1 and 2 in the vertices array.

Since you're using a mesh normals material, you might want to compute normals for the geometry. Also, make sure your object can be visible (is not to big or to close to the camera to be clipped out, is facing the right direction - towards the camera, etc.) Since you're drawing in the YZ plane, to see your triangle, something like this should work:

```
var geom = new THREE.Geometry();
var v1 = new THREE.Vector3(0,0,0);
var v2 = new THREE.Vector3(0,500,0);
var v3 = new THREE.Vector3(0,500,500);
geom.vertices.push(v1);
geom.vertices.push(v2);
geom.vertices.push(v3);
geom.faces.push( new THREE.Face3( 0, 1, 2 ) );
geom.computeFaceNormals();
var object = new THREE.Mesh( geom, new THREE.MeshNormalMaterial() );
object.position.z = -100;//move a bit back - size of 500 is a bit big
object.rotation.y = -Math.PI * .5;//triangle is pointing in depth, rotate it -90 degrees on Y
scene.add(object);
```

For big polygons it can be quite a job to manually add the faces. You can automate the process of adding faces to the mesh using the `triangulateShape`

method in `THREE.ShapeUtils`

like this:

```
var vertices = [your vertices array];
var holes = [];
var triangles, mesh;
var geometry = new THREE.Geometry();
var material = new THREE.MeshBasicMaterial();
geometry.vertices = vertices;
triangles = THREE.ShapeUtils.triangulateShape( vertices, holes );
for( var i = 0; i < triangles.length; i++ ){
geometry.faces.push( new THREE.Face3( triangles[i][0], triangles[i][1], triangles[i][2] ));
}
mesh = new THREE.Mesh( geometry, material );
```

Where `vertices`

is your array of vertices and with `holes`

you can define holes in your polygon.

**Note:** Be careful, if your polygon is self intersecting it will throw an error. Make sure your vertices array is representing a valid (non intersecting) polygon.

THREE.Vertex has been deprecated in the newest version of Three.js so that part is not needed anymore:

```
geom.vertices.push(v1);
geom.vertices.push(v2);
geom.vertices.push(v3);
```

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