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. 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.

Whether it is moving or not, the Camera3D has the ability to look in any direction from its current position. (This need not be the same direction as that in which the camera is moving.) One of the ways we can specify the camera's orientation is by yaw, pitch, and roll, concepts arising from (aero)nautical navigation.

• Yaw, or heading, is rotation about the vertical axis at the camera position (in Sandy, this is an axis parallel to the Y axis). If the camera is positioned at the center of the Earth, you can think of yaw as the longitude of the point it is looking at. We define yaw to be zero when the camera is looking in the +Z direction. (In aeronautics, a heading of zero indicates the airplane is facing north.) In Sandy 0.2, this is implemented by Camera3D's rotateY() method.

• Pitch is rotation of the line of sight up or down from the horizontal plane at the camera position (in Sandy, this is a plane parallel to the XZ plane). If the camera is positioned at the center of the Earth, you can think of pitch as the latitude of the point it is looking at. Pitch is not implemented in Sandy 0.2, but it is planned for the 0.3 release. For the time being you can use the tilt() method, which will be equivalent to pitch as long as you don't use roll() at all!

• Roll is not a change of direction per se. It is rotation around the line of sight itself. It's like cocking your head to one side or the other. In Sandy 0.2 this is implemented by Camera3D's roll() method. (Camera3D does have a rotateZ() method but it would seem to be of limited usefulness.) A roll operation does not change the effect of subsequent yaw or pitch operations.

The above concepts depend on having a notion of “which way is up.” But in deep space there may be no such concept. In this case we can use pan and tilt instead of yaw and pitch. (Roll remains the same.) Pan and tilt are implemented in Sandy by Camera3D methods with those exact names. A roll operation will change the effect of subsequent pan and tilt operations.

Pan and tilt can be thought of as rotations in the camera's local frame of reference, as opposed to yaw and pitch which are defined in terms of global directions. In consequence, the idea of current values of pan and tilt (and roll in this context) has meaning only in relation to some initial orientation, while the idea of current values of yaw and pitch (and roll in this context) has a constant meaning that never changes.

A simple comparison may help to show the difference. If you set pitch to 90 degrees, you are facing straight up. If you then yaw by any amount, you are still facing straight up but you are rotating your view. When pitch is 90 degrees, yaw has the same effect as roll, since the view axis is the vertical axis. On the other hand, there is no tilt that can put you into an orientation where pan becomes the same as roll. In fact, if you start at the default orientation (facing towards positive Z with positive Y at the top of your view) and tilt up 90 degrees then pan left 90 degrees, you will not only be facing in the negative X direction but the top of your view will be negative Z! Intergalactic pilots will have a feel for this kind of navigation; the rest of us will probably want to stick to yaw and pitch.