# Projection types,View volumes,Viewing projection
###### tags: `course` `computer graphic`
## Projection types

* Parallel projection
> 好算
* Perspective projection
> 常用
## View volumes
- A camera position C and a viewing direction vector N (= view plane normal ), and an upvector V
- A view plane distance d
- A near clipping plane distance n, and a far clipping plane distance f.

* Parallel projection
> 好算

* Perspective projection

* View coordinate system (u, v, n)
>　v=V, n=-N, u=v x n, where V is perpendicular to n
>　v = up vector
>　n = view direction


## Viewing projection

* View transformation: Tview
> World coordinate to view (eye) coordinate，方便clippng和projection
> Tview = B T
> B =>rotate to map (u,v,n) to (e1,e2,e3)
> T translate world origin coordinate to camera position C
* View projection: Tp
> view coord. to normalized device coord. sys
> view volume -> normalized view volume do orthogonal projection
> Tp = Tpers1 Tpers2
> Easy view-volume clipping, back-face culling, and projection

* clipping and normalized coordinate