Hugging the terrain...face normals

Need to get the dozer to hug the slope of the terrain so it doesn't move up and down like an 'elevator' when moving across rough terrain.

Essentially that ray that I shoot down through the dozer to the ground to determine height, I am also going to determine the 'normal' (perpendicular) to the ground poly and rotate the dozer accordingly.  Theoretically I should sample ALL the ground under the dozer to determine the ultimate rotation, but this will work for now.

                oldrot = dozer.rotation.y;

                /store the old 'y' rotation because we are going to use it later...only X and Z will change to hug the ground

                intersects = ray.intersectObject(plane);

                if ( intersects.length > 0 ) {

                    dozer.position.y = (intersects[ 0 ].point.y);

                    // get the face normal in object space

                    var vec = intersects[0].face.normal.clone();

                     //  points up 

                    var up = new THREE.Vector3( 0, 1, 0 );

                    //  we want the dozer to face in the direction of the face normal

                    // cross will not work if vec == +up or -up, so there is a special case

                   if ( vec.y == 1 || vec.y == -1 ) {

                        var axis = new THREE.Vector3( 1, 0, 0 );

                    }

                    else {

                        var axis = new THREE.Vector3().cross( up, vec );

                    }

                    // determine the amount to rotate

                    var radians = Math.acos( vec.dot( up ) );

                    // create a rotation matrix that implements that rotation

                    var mat = new THREE.Matrix4().setRotationAxis( axis, radians );

                    // apply the rotation to the dozer

                    getRotationFromMatrix( dozer.rotation,mat, dozer.scale );

                    //put back to original y rotation.

                    dozer.rotation.y=oldrot;

                }