In Sandy, the axis disposition is as follows :

• x axis is the side vector. It is the axis joining your shoulders. As you move to the right, the x value is increasingly positive.

• y axis is the vertical vector. It is the axis joining your feet and your head. The positive way is up (toward your head); the negative way is down (toward your feet).

• z axis is the depth vector. It is the axis projected from your eyes. What you see in front of you is the positive way (increasing z); what is behind you is the negative direction (we back the camera to a negative z in order to “zoom out”).

Sandy uses a left-handed coordinate system. This means that you can visualize it by holding the thumb, index, and middle fingers of your left hand at right angles to one another. First, make an “L” with your left hand's index finger and thumb. Then point your middle finger away from you. The X axis is your thumb, the Y axis your index finger, and the Z axis is your middle finger. The positive X direction is to the right, the positive Y direction is up, and the positive Z direction is straight ahead.

Here's a simple picture to illustrate the reference frame: