Joint positions and orientations are given in the real world coordinate system.The origin of the system is at the sensor. +X points to the right of the, +Y points up, and +Z points in the direction of increasing depth. The coordinate frame is shown in the figure above.
關節的位置和方向依據于現實世界的坐標系統。坐標原點定位在Sensor。X軸的正方向是人體面對Sensor的右方。Y軸的正方向是朝上。Z軸的正方向是深度值增加的方向。（綜合而看，這是一個典型的右手坐標系）
Joint positions are measured in units of mm.
關節的位置是以毫米為單位來衡量的。
Joint orientations are given as a 3x3 rotation (orthonormal) matrix. This represents a rotation between the joint's local coordinates and the world coordinates.
The first column is the direction of the joint's +X axis given as a 3-vector in the world coordinate system.
The second column is the +Y axis direction, and the third column is the +Z axis direction.
Our “neutral pose” is the T-pose shown in the figure above. In this pose, each joint's orientation is aligned with the world coordinate system. That is, its orientation is the identity matrix.
關節的方向依據于一個3x3的旋轉（正交）矩陣。這個矩陣描繪的是關節的局部坐標和世界坐標之間的旋轉。
矩陣的第一列代表的是關節X軸的正方向，一個在世界坐標系里的 3-Vector.
矩陣的第二列代表的是關節Y軸的正方向，矩陣的第三列代表的是關節Z軸的正方向。
我們的"neutral pose"是一個T-姿勢，如上圖所示。在這個姿勢中，每個關節的方向是一致的與世界坐標系。也就是說，它的方向是單位矩陣。
Known issues 已知問題
1. Arm tracking is less stable when the arm is close to other body parts, especially the torso. If both arms are close to the torso, as well as to each other, they might get mixed up.
在手臂貼近身體的其它部位時（特別是軀干），手臂跟蹤的穩定性會較差。如果雙臂非常接近軀干以及對方的話，那么它們也可能會混淆在一起。
2. Leg tracking is still somewhat unstable and noisy. It works better when the user stands with legs separated. Fast motions and complex kicks or crouches might cause the tracking to fail.
腿的跟蹤一直有一些不穩定和干擾。當用戶把雙腿分開站立時，跟蹤的效果會更好?？焖俚倪\動和復雜的踢或蹲可能會導致跟蹤失敗。
3. Pose tracking may also become somewhat unstable if the head is not visible.
如果頭是不可見的話，那么姿態跟蹤也會變得不穩定。
4. Arms and legs in extremely stretched positions (i.e. near the limits of human flexibility) might be lost by the tracker.
當手臂和腿處于極限拉伸的位置時（比如達到了人體靈活性的極限），可能會丟失跟蹤。
5. If the skeleton is stuck in a faulty pose, or stuck facing the opposite direction, then returning to a “simple” pose (arms away from torso so the sensor can see them and legs separated) should help resolve it.
如果骨骼卡住在一個錯誤的姿態，或者面向相反的方向，那么請回到一個簡單的姿勢（如：手臂遠離軀干，雙腿分開站立。）這些會幫助解決被卡住的問題。
6. In general, very fast motions may cause tracking failure.
在一般情況下，速度非常快的運動可能會導致跟蹤失敗。
7. In some cases, overall tracking might be bad. Re-calibrating the user may resolve the problem.
在某些情況下，整體跟蹤的效果可能不太好。那么重新"Calibrating"會解決問題。
來自：http://www.cnblogs.com/TravelingLight/archive/2011/04/18/2019887.html