通常情况下，3-D 图形应用程序使用两种卡笛尔坐标系：左手系和右手系。在这两种坐标系下，X 轴的正向指向右方，Y 轴正向指向上方。你可以这样记忆 Z 轴的正向：无论是左手系还是右手系，将你的手指沿 X 轴的正向伸展开，然后向 Y 轴的正向弯曲，这样你的大拇指所指的方向就是 Z 轴的正向。下面的插图就显示了这两个坐标系。
Typically 3-D graphics applications use two types of Cartesian coordinate systems: left-handed and right-handed. In both coordinate systems, the positive x-axis points to the right, and the positive y-axis points up. You can remember which direction the positive z-axis points by pointing the fingers of either your left or right hand in the positive x-direction and curling them into the positive y-direction. The direction your thumb points, either toward or away from you, is the direction that the positive z-axis points for that coordinate system. The following illustration shows these two coordinate systems.
Direct3D 使用的是左手坐标系。如果你正在移植基于右手系的应用程序时，你必须对传给 Direct3D 的数据做两方面的修改：
Microsoft® Direct3D® uses a left-handed coordinate system. If you are porting an application that is based on a right-handed coordinate system, you must make two changes to the data passed to Direct3D.
颠倒三角形顶点的顺序，这样系统可以从正面沿顺时针的方向去遍历他们。换句话说就是，如果原顶点的顺序为v0、v1、v2，那么将他们传递给 Direct3D 时就应该以这样的顺序v0、v2、v1。
用观察矩阵对世界空间中 Z 轴上的值求反。为了达到这个目的，将观察矩阵中的 D3DMATRIX 结构中的_31、_32、_33 和 _34 成员的符号取反。
Use the view matrix to scale world space by -1 in the z-direction. To do this, flip the sign of the _31, _32, _33, and _34 member of the D3DMATRIX structure that you use for your view matrix. 要得到右手系世界空间的效果，要使用 D3DXMatrixPerspectiveRH 和 D3DXMatrixOrthoRH 函数来定义投影矩阵的转换。但是，要小心使用对应的 D3DXMatrixLookAtRH 函数，反转背景裁剪的顺序，以及立方体贴图的位置。
To obtain what amounts to a right-handed world, use the D3DXMatrixPerspectiveRH and D3DXMatrixOrthoRH functions to define the projection transform. However, be careful to use the corresponding D3DXMatrixLookAtRH function, reverse the backface-culling order, and lay out the cube maps accordingly.
虽然左手系和右手系都是很常用的系统，但是也有很多其他种类的坐标系用于 3-D 软件。比如说，对于3-D 建模应用程序而言，Y 轴指向或背向观察者的坐标系就并不罕见。在这种情况下，右手系就定义为任意轴的正向均指向观察者。而左手系就定义为任意轴的正向均背向观察者。如果你正在移植 Z 轴指向上的左手系建模应用程序，你就必须将所有的顶点数据做上述的处理。
Although left-handed and right-handed coordinates are the most common systems, there is a variety of other coordinate systems used in 3-D software. For example, it is not unusual for 3-D modeling applications to use a coordinate system in which the y-axis points toward or away from the viewer, and the z-axis points up. In this case, right-handedness is defined as any positive axis (x, y, or z) pointing toward the viewer. Left-handedness is defined as any positive axis (x, y, or z) pointing away from the viewer. If you are porting a left-handed modeling application where the z-axis points up, you must do a rotation on all the vertex data in addition to the previous steps.
对 3-D 坐标系中定义的对象最基本的操作就是变换、旋转和缩放。你可以将基本变换进行组合，以此来创建出新的变换矩阵。更多细节请查看 3-D 变换。
The essential operations performed on objects defined in a 3-D coordinate system are translation, rotation, and scaling. You can combine these basic transformations to create a transform matrix. For details, see 3-D Transformations.
当你在组合这些操作的时候，矩阵的运算顺序是不可交换的，不同相乘顺序会导致不同的变换效果，这点很重要。
When you combine these operations, the results are not commutative - the order in which you multiply matrices is important.
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