cameraProjection

Camera projection matrix

Since R2022b

Description

example

camProjection = cameraProjection(intrinsics,tform) returns a 3-by-4 camera projection matrix camProjection. You can use camProjection to project a 3-D world point in homogeneous coordinates into an image according to the transformation tform.

Examples

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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.

imageSize = [size(I,1) size(I,2)];
cameraParams = estimateCameraParameters(imagePoints,worldPoints,ImageSize=imageSize);
intrinsics = cameraParams.Intrinsics;

Load an image at a new location.

figure
imshow(imOrig)
title("Input Image")

Undistort the image.

[im,newOrigin] = undistortImage(imOrig,intrinsics,OutputView="full");

Find the reference object in the new image.

[imagePoints,boardSize] = detectCheckerboardPoints(im);

Compensate for the image coordinate system shift.

imagePoints = imagePoints+newOrigin;

Calculate new extrinsics.

camExtrinsics = estimateExtrinsics(imagePoints,worldPoints,intrinsics);

Calculate the camera projection matrix.

P = cameraProjection(intrinsics,camExtrinsics)
P = 3×4
105 ×

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

Input Arguments

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Camera intrinsics, specified as cameraIntrinsics object. The object stores information about a camera’s intrinsic calibration parameters, including the lens distortion parameters.

Transformation from world coordinates to camera coordinates, specified as a rigidtform3d object. You can use the estimateExtrinsics function to create the tform object. The R and Translation properties of the object represent the rotation matrix and translation needed to project 3-D world points in homogeneous coordinates into an image.

Output Arguments

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Camera projection matrix, returned as a 3-by-4 matrix. The matrix contains the 3-D world points in homogenous coordinates that are projected into the image.

The function calculates camProjection using the intrinsic matrix K and the R and Translation properties of the tform object as follows:

camProjection = K × [tform.R tform.Translation']

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

w × [x,y,1]' = camProjection× [X,Y,Z,1]'

 (X,Y,Z) are the world coordinates of a point (x,y) are the coordinates of the corresponding image point w is an arbitrary scale factor

When the R and Translation properties of the transformation tform are of data type double, the function returns camProjection as double. Otherwise the function returns camProjection as single.

Data Types: single | double

Version History

Introduced in R2022b

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