loadCamera( cameraIndex ) {

		let camera;
		const cameraDef = this.json.cameras[ cameraIndex ];
		const params = cameraDef[ cameraDef.type ];

		if ( ! params ) {

			console.warn( 'THREE.GLTFLoader: Missing camera parameters.' );
			return;

		}

		if ( cameraDef.type === 'perspective' ) {

			camera = new PerspectiveCamera( MathUtils.radToDeg( params.yfov ), params.aspectRatio || 1, params.znear || 1, params.zfar || 2e6 );

		} else if ( cameraDef.type === 'orthographic' ) {

			camera = new OrthographicCamera( - params.xmag, params.xmag, params.ymag, - params.ymag, params.znear, params.zfar );

		}

		if ( cameraDef.name ) camera.name = this.createUniqueName( cameraDef.name );

		assignExtrasToUserData( camera, cameraDef );

		return Promise.resolve( camera );

	}
Specification: https://github.com/KhronosGroup/glTF/tree/master/specification/2.0#cameras

@private
@param {number} cameraIndex
@return {Promise<THREE.Camera>}