# Walking on a sphere

I'm working on a game which involves walking your character on the surface of a sphere. Using the answer to Arbitrary Rotation about a Sphere, I've written my code as:

``````if (game.isKeyDown(37)) { // left
this.quaternion.multiply(new THREE.Quaternion(0, Math.sin(-0.01), 0, Math.cos(-0.01)));
}

if (game.isKeyDown(39)) { // right
this.quaternion.multiply(new THREE.Quaternion(0, Math.sin(0.01), 0, Math.cos(0.01)));
}

if (game.isKeyDown(38)) { // up
this.quaternion.multiply(new THREE.Quaternion(Math.sin(-0.01), 0, 0, Math.cos(-0.01)));
}

if (game.isKeyDown(40)) { // down
this.quaternion.multiply(new THREE.Quaternion(Math.sin(0.01), 0, 0, Math.cos(0.01)));
}

var qx = this.quaternion.x;
var qy = this.quaternion.y;
var qz = this.quaternion.z;
var qw = this.quaternion.w;
this.obj.position.x = 2 * (qy * qw + qz * qx) * radius;
this.obj.position.y = 2 * (qz * qy - qw * qx) * radius;
this.obj.position.z = ((qz * qz + qw * qw) - (qx * qx + qy * qy)) * radius;
``````

Which works fine, however I would like to control the character in such a way that pressing up and down is equivelent to walking forwards and backwards (in the direction you are looking), whereas pressing left and right is the same as turning around on the spot.

I understand that I will have to store a forward vector, but I'm not clear on how that relates to the quaternion which allows the character to walk on the surface of the sphere.

Another problem I've got to overcome is making sure the character on the surface of the sphere is actually "looking" the way it is going, at the moment I'm modelling the player as another sphere, but in the futuer it will be a proper model which will need to orientate itself.

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