vision Flashcards
How to define the camera position
The camera position can be defined by a translation [Tx, Ty,Tz] and a rotation in the 3D space which is represented by 3*3 matrix
How to define the reotation in the 3D space
it can be defined by 3 values, euler angles that can be represented by a 33 matrix, know that all the 3D rotations can be represented by a 33 matrix but not all the 3*3 matrices are 3D rotations
what are the Euler angles
the describe 3angles that define the orientation of a rigid body
what are the extrinsic parameters
correspond to the combination of the rotation and translation to define the camera
what is the main idea behind a pinhole camera
project 3D points in the space to a 2D one, such that every 3D point is represented by 2 points of the sensor
what is the difference between extrinsic and intrinsic parameters
extensive is more related to the camera position and intensity are more related to the project of the points in the space
what is the focal length
it is the distance between the the lens and the sensor , we use it to represent the sensor points in term of space points
how can we represent the world coordinates to pixel coordinates
one can use the mixture of intrinsic and extrinsic parameters
explain the stereovision settings
The image is seen by two cameras, they are both on the same epipolar line, the distance between them is called the baseline and their optical view is parallel to each other
why the angle of the eye change and is not parallel all the time
through constantly modifying the angles leads to obtain wider fields between the intersection of the cameras projection
why we may need the stereovision
stereovision allows acquiring the geometry of the object
what is the disparity
reflects the difference in the projection
what is the relation between the distance and the dipary
The higher is the distance the higher is the disparity
How the objects are detecion happen
the idea is that when both camera projections meet, that field is captured
How the objects are detected happen
the idea is that when both camera projections meet, that field is captured
what is the relation between the disparity and the baseline
the lower is the baseline the lower is the disparity, the higher is the baseline the lower is the coverage and the higher is the accuracy
why camera with fixed angles
a camera with fixed angles is less complex to deal
how to build a disparity map
we need to perform point matching
why increasing the baseline means increasing the accuracy
This is a matter of scale
How to perform point matching
The idea is that we have a window that is horizontally moving throughout the acquired images, then the matching happens in the case of the part corresponding to the lowest SSD
how to deal with the noise during point matching
this might be due to the size of the window hence increasing the noise might be a solution however this also leads to lose some of the details
how to deal with the noise during point matching
this might be due to the size of the window hence increasing the noise might be a solution however this also leads to losing some of the details
what is epipolar plane
it is a plane that joins the points of the space in the front of the camera and the two points of projection, this plane makes an intersection with the projection planes and outputs the epipolar lines
what is the epipolar line for parallel camera
it is horizontal
what are the intrinsic parameters
The Camera constant (C): describes the distance between the image plane and the projection centre.
x-y scale difference m
focal length f,
initially, the points of the space are projected to the sensor and are represented in terms of the focal loss, however, we may need to take into consideration the fact that :
- camera’s pixels may not be squared hence, fx,fy
- the optical center is not always 0 (cx,cy)
- skewness: the camera sensor may have skew in the x,y
why the higher is the baseline the higher is the accuracy
since a higher baselin we can capture more depth thus more accuracy
what is the relation between epipolar line and depth
epipolar line allow us to measure the depth
