The definition of the view point

The calculation of the projection transformation requires that a view point and a view direction are first specified. These can be called the eye position and the line of sight. In general, these can be any position and any direction. To present a simpler model for the purposes of this tutorial, only view directions that point towards the origin will be considered. This allows the eye position and line of sight to be defined in one viewing vector.

The viewing vector is defined in world coordinates, but to allow easier definition of different views relative to the world coordinate origin polar coordinates are often used. The relationship between the viewing vector and the world coordinate system is shown in Figure 1.1. The eye coordinate system is shown in red, whilst the world coordinate system is shown in black.

You can rotate the image by dragging the mouse across it with the left mouse button held down.

Figure 1.1:The viewing vector

Now that we have a way of specifying a view position and direction, the next stage is to calculate the viewing transformation operations needed to form a projected image.

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