原始的材质贴图坐标和高度数据已经在切线空间中了，因此视向量最好也能如此。

The original texture coordinate and height values are already represented in tangent space, so the eye vector must be as well.

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视向量能够在全局坐标系中通过视点坐标减去表面坐标来创建，并且要把结果转换到切线空间中。

The eye vector can be created in global coordinates by subtracting a surface position from the eye position and transforming the resulting vector into tangent space.

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本文在T．L．坐标下，利用能量原理，同时导出了空间杆元精确的割线刚度矩阵和切线刚度矩阵显式。

In this paper, the tangent stiffness matrices and the secant stiffness matrices of space trusses are derived with the energy principle in the Total Lagrangian coordinates.

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