Seonglae ChoProjective Matrix
Scene should planar and very far or has little depth variation (approximately planar)
두 평면 사이의 변환을 나타내는 행렬
여러 장의 이미지를 스티칭하여 하나의 큰 이미지로 만들 때 사용
Degree of freedom is 8 (3x3 Homography matrix, 1 scale)
so we need at least 4 points (2 equations resulted from below eqation)
Image Homography Notion