camera model

3D Viewing: the Pinhole Camera Model (How a pinhole camera works (part 1)) (scratchapixel.com)

https://web.stanford.edu/class/cs231a/course_notes.html

3. lock_at 函数

http://www.euclideanspace.com/maths/algebra/vectors/lookat/

https://www.scratchapixel.com/lessons/mathematics-physics-for-computer-graphics/lookat-function