cameraMatrix

Camera projection matrix

Syntax

camMatrix = cameraMatrix(cameraParams,tform)

camMatrix = cameraMatrix(cameraParams,rotationMatrix,translationVector)

Description

camMatrix = cameraMatrix(cameraParams,tform) returns a 4-by-3 camera projection matrix camMatrix, which can be used to project a 3-D world point in homogeneous coordinates into an image. cameraParams can be a cameraParameters object or a cameraIntrinsics object.

camMatrix = cameraMatrix(cameraParams,rotationMatrix,translationVector) returns a 4-by-3 camera projection matrix. You can use this matrix to project 3-D world points in homogeneous coordinates into an image.

Examples

Compute Camera Matrix

Create a set of calibration images.

images = imageDatastore(fullfile(toolboxdir('vision'),'visiondata', ...
    'calibration','slr'));

Detect the checkerboard corners in the images.

[imagePoints,boardSize] = detectCheckerboardPoints(images.Files);

Generate the world coordinates of the checkerboard corners in the pattern-centric coordinate system, with the upper-left corner at (0,0). The square size is in millimeters.

squareSize = 29; 
worldPoints = generateCheckerboardPoints(boardSize,squareSize);

Calibrate the camera.

I = readimage(images,1); 
imageSize = [size(I,1),size(I,2)];
cameraParams = estimateCameraParameters(imagePoints,worldPoints, ...
                                       'ImageSize',imageSize);

Load image at new location.

imOrig = imread(fullfile(matlabroot,'toolbox','vision','visiondata', ...
      'calibration','slr','image9.jpg'));
figure; imshow(imOrig);
title('Input Image');

Undistort image.

im = undistortImage(imOrig,cameraParams);

Find reference object in new image.

[imagePoints,boardSize] = detectCheckerboardPoints(im);

Compute new extrinsics.

[rotationMatrix,translationVector] = extrinsics(...
    imagePoints,worldPoints,cameraParams);

Calculate camera matrix

P = cameraMatrix(cameraParams,rotationMatrix,translationVector)

P = 4×3
105 ×

    0.0157   -0.0271    0.0000
    0.0404   -0.0046   -0.0000
    0.0199    0.0387    0.0000
    8.9399    9.4399    0.0072

Input Arguments

cameraParams — Object for storing camera parameters

cameraParameters object | cameraIntrinsics object

Camera parameters, specified as a cameraParameters or cameraIntrinsics object. You can return the cameraParameters object using the estimateCameraParameters function. The cameraParameters object contains the intrinsic, extrinsic, and lens distortion parameters of a camera.

tform — Transformation

rigid3d object

Transformation from world coordinates to camera coordinates, specified as a rigid3d object. You can use the extrinsics function to obtain the rotation and translation to create the tform object.

rotationMatrix — Rotation of camera

3-by-3 matrix

Rotation of camera, specified as a 3-by-3 matrix. You can obtain this matrix using the extrinsics function. You can also obtain the matrix using the relativeCameraPose function by transposing its orientation output. The rotationMatrix and translationVector inputs must be real, nonsparse, and of the same class.

translationVector — Translation of camera

1-by-3 vector

Translation of camera, specified as a 1-by-3 vector. The translation vector describes the transformation from the world coordinates to the camera coordinates. You can obtain this vector using the extrinsics function. You can also obtain the vector using the location and orientation outputs of the relativeCameraPose function:

• translationVector = -relativeLocation * relativeOrientation'

The translationVector inputs must be real, nonsparse, and of the same class.

Output Arguments

camMatrix — Camera projection matrix

4-by-3 matrix

Camera projection matrix, returned as a 4-by-3 matrix. The matrix contains the 3-D world points in homogenous coordinates that are projected into the image. When you set rotationMatrix and translationVector to double, the function returns camMatrix as double. Otherwise it returns camMatrix as single.

The function computes camMatrix as follows:

camMatrix = [rotationMatrix; translationVector] × K.
K: the intrinsic matrix

Then, using the camera matrix and homogeneous coordinates, you can project a world point onto the image.

w × [x,y,1] = [X,Y,Z,1] × camMatrix.

(X,Y,Z): world coordinates of a point

(x,y): coordinates of the corresponding image point

w: arbitrary scale factor

Data Types: single | double

Extended Capabilities

C/C++ Code Generation

Generate C and C++ code using MATLAB® Coder™.

Usage notes and limitations:

• Use in a MATLAB Function block is not supported.

Version History

Introduced in R2014b