3. The Camera - Our window into the world

The `camera' is central to the raytracing process. It represents the viewer in the scene. It forms the origin from where all the rays are shot. Given
below is a description of how the camera (or view) coordinate system is aligned with respect to the world coordinate system.

1. The Coordinate System -
   The view coordinate system has its origin at the view_coordinate_center. The eye is the actual location of the camera. The view coordinate axes u and v
   are oriented according to the up_vector. The up_vector tells the system which direction is the positive u-axis with respect to the world coordinate system.
   The look_at vector is point at which the viewer wants to look (the center of his view) in the world coordinate system. The view_ direction is now calculated
   as the vector from the view_coordinate_center to the look_at point. This is the direction along which the n-axis of the view coordinate system gets aligned.
   The image is formed at the origin of the view coordinate system in the u-v plane.
   Figure 1
   
   
2. Camera Specification -
   The camera is to be specified by the user in the scene file. It consists of the following parameters -
   1. View Coordinate Center (in world coordinates)
   2. Eye (in view coordiantes)
   3. Up Vector (in world coordinates)
   4. Look At point (in world coordinates)
   5. Far Plane distance (in world coordinates)
   6. Horizontal Field of View (in degrees)
   7. Vertical Field of View (in degrees)
   The various parameters can be understood with the help of the figures 1 and 2. A sample camera specification is also given.
   Figure 2
   A sample camera specification in a scene file -

   camera
   {
     -100.0 100.0 150.0 1.0
     0.0 0.0 -20.0 1.0
     0.0 1.0 0.0 1.0
     50.0 50.0 0.0 1.0
     1000.0
     45.0
     45.0
   }
   

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