# How do you find the epipolar line?

## How do you find the epipolar line?

Similar to the Essential matrix, we can compute the epipolar lines l = FT p and l = Fp from just the Fundamental matrix and the corresponding points.

## What does it mean when your epipolar lines a cross?

The epipole is the point of intersection of the line joining the optical centres, that is the baseline, with the image plane. Thus the epipole is the image, in one camera, of the optical centre of the other camera. The epipolar plane is the plane defined by a 3D point M and the optical centres C and C’.

**What is epipolar image?**

Epipolar images are stereo pairs in which the left and right images are oriented in such a way that ground feature points have the same y-coordinates on both images.

**Are epipolar lines parallel?**

In the case of a special motion where the translation is parallel to the image plane, and the rotation axis is perpendicular to the image plane, the intersection of the baseline with the image plane is at infinity. Consequently the epipoles are at infinity, and epipolar lines are parallel.

### What does it mean when epipolar lines are horizontal?

This means that for each point in one image, its corresponding point in the other image can be found by looking only along a horizontal line.

### Why is the fundamental matrix rank 2?

It is not a full rank matrix, so it is singular and its determinant is zero (Proof here). The reason why F is a matrix with rank 2 is that it is mapping a 2D plane (image1) to all the lines (in image 2) that pass through the epipole (of image 2).

**Why is the epipolar constraint useful?**

The epipolar constraint is one of the fundamental relations in multi-view geometry because it allows the estimation of the 3D coordinates of point p from its images x1 and x2, given R and T. That is, it allows scene geometry reconstruction.

**What is disparity map?**

Disparity map refers to the apparent pixel difference or motion between a pair of stereo images. To experience this, try closing one of your eyes and then rapidly close it while opening the other. Objects that are close to you will appear to jump a significant distance while objects further away will move very little.

#### Do epipolar lines converge?

If the image planes are aligned and their optical axes are parallel, the two epipolar lines (left and right) converge.

#### What is the difference between fundamental matrix and essential matrix?

Thus both the Essential and Fundamental matrices completely describe the geometric relationship between corresponding points of a stereo pair of cameras. The only difference between the two is that the former deals with calibrated cameras, while the latter deals with uncalibrated cameras.

**Why does fundamental matrix have 7 degrees of freedom?**

So, if we work out only 7 of the 9 parameters of the fundamental matrix, we can work out the last parameter using the above determinant equation. Therefore the fundamental matrix has 7DOF. Simply the essential matrix (E) is the fundamental matrix taking into account the camera intrinsic parameters.

**What should a disparity map look like?**

## How is disparity map calculated?

Calculating Disparity Map First, squared difference or absolute difference is calcluated for each pixel and then all the values are summed over a window W. For each shift value of the right image, there is an SSD/SAD map equal to the size of the image. The disparity map is a 2D map reduced from 3D space.

## What is projection matrix of camera?

In computer vision a camera matrix or (camera) projection matrix is a. matrix which describes the mapping of a pinhole camera from 3D points in the world to 2D points in an image.

**Why do we need 8 points to estimate the fundamental matrix?**

Unlike a homography, where each point correspondence contributes two constraints (rows in the linear system of equations), for estimating the essential/fundamental matrix, each point only contributes one constraint (row). [because the Longuet-Higgins / Epipolar constraint is a scalar eqn.] Thus need at least 8 points.

**What is the purpose of fundamental matrix?**

The fundamental matrix is used to express the state-transition matrix, an essential component in the solution of a system of linear ordinary differential equations.

### How do you create a disparity map?

A simple solution when creating a disparity map the largest distance becomes black ie rgb(0,0,0) and the smallest distance – which is 0 – becomes white ie rgb(255,255,255). If you divide 255 by the largest distance then you find the increment value.

### What is the difference between depth map and disparity map?

Disparity is the horizontal displacement of a point’s projections between the left and the right image. Whereas, depth refers to the z coordinate (usually z) of a point located in the real 3D world (x, y, z).

**What are camera coordinates?**

Normalized camera matrix and normalized image coordinates So far all points in the 3D world have been represented in a camera centered coordinate system, that is, a coordinate system which has its origin at the camera center (the location of the pinhole of a pinhole camera).