Lecture 3 Flashcards
What is the World/Object coordinate system?
Coordinate system provides a reference point which describes the position of the camera in real-world space.
This reference point remains stationary as the device moves.
What is the Camera System
This is a coordinate system that uses the camera centre as its origin.
What is the Image/Retinal plane coordinate system
Plane on which the image is
formed (film), note that the image plane is measured in camera
frame coordinates (mm).
What is the image Frame coordinate system?
A coordinate system that measures pixel locations on the image plane.
What are the 4 main types of coordinate systems?
- World / object coordinate system
- Camera System
- Image or Retinal Plane coordinate system
- Image Frame Coordinate System
What is a projective transformation?
When point P in a 3D space is mapped to a 2D point P’ on the image plane.
R^3 –> R^2
What is the main issue with projection modelling?
Points in the digital image are generally in a different reference system than those in the image plane.
Also, Digital images are divided into discrete pixels, while points in the image plane are continuous.
What is the Camera Reference Model?
It describes a set of parameters that affect how a world point P is mapped to image coordinate P’
The first parameters Cx and Cy describe how the image plane and digital image coordinates can differ by a translation.
What are the intrinsics of a camera?
They describe how a point in the 3D world is mapped onto the 2D image plane
What are the intrinsic parameters?
Scale Factor
Focal Length
Skew
Principle Point
Distortion (lens)
Define what skew is, one of the intrinsic parameters
Skew is when the principle point is not exactly at the centre of the image plane. The camera has to take this into account.
What is the extrinsic matrix?
The extrinsic matrix defines the loaction and orientation of the camera with respect to the world frame.
It contains 6 parameters: Rotation (3) and Translation (3)
What is the translation vector?
The translation Vector refers to the position of the camera in regards to the world origin. It is one of the Extrinsic parameters of a camera
What is Rotation in relation to the extrinsic matrix?
The Rotation parameter is 3 x 3 matrix describing the rotational mapping from the world coordinate frame into the camera coordinate frame.
What is the Perspective Camera Model?
Given matrix M, we can map from 3D point P in a random world reference system to 2D point P’ on the image plane.
P’2D = K[R][t]P3D = M3x4P3D
