estimateCheckerboardCorners3d

Estimate world frame coordinates of checkerboard corner points in image

Syntax

imageCorners3d = estimateCheckerboardCorners3d(I,cameraIntrinsic,checkerSize)

[imageCorners3d,boardDimensions] = estimateCheckerboardCorners3d(I,cameraIntrinsic,checkerSize)

[___,imagesUsed] = estimateCheckerboardCorners3d(imageFileNames,cameraIntrinsic,checkerSize)

[___] = estimateCheckerboardCorners3d(imageArray,cameraIntrinsic,checkerSize)

[___] = estimateCheckerboardCorners3d(___,Name,Value)

Description

imageCorners3d = estimateCheckerboardCorners3d(I,cameraIntrinsic,checkerSize) estimates the world frame coordinates of the corner points of a checkerboard in an image, I, by using the camera intrinsic parameters cameraIntrinsic and the size of the checkerboard squares checkerSize.

[imageCorners3d,boardDimensions] = estimateCheckerboardCorners3d(I,cameraIntrinsic,checkerSize) additionally returns the checkerboard dimensions boardDimensions.

[___,imagesUsed] = estimateCheckerboardCorners3d(imageFileNames,cameraIntrinsic,checkerSize) estimates the world frame coordinates of the corner points of a checkerboard from a set of image files, imageFileNames. The function returns a logical vector that indicates in which images it detected a checkerboard, imagesUsed, in addition to any combination of output arguments from previous syntaxes.

[___] = estimateCheckerboardCorners3d(imageArray,cameraIntrinsic,checkerSize) estimates the world frame coordinates of the corner points of a checkerboard from an array of images, imageArray.

[___] = estimateCheckerboardCorners3d(___,Name,Value) specifies options using one or more name-value pair arguments in addition to any combination of arguments from previous syntaxes. For example, 'MinCornerMetric',0.2 sets the threshold for the checkerboard corner metric to 0.2.

Examples

Detect Checkerboard Corners in Image

Detect a checkerboard in an image using the estimateCheckerboardCorners3d function and estimate the world frame coordinates of the checkerboard corners.

Read the image into the workspace.

Image = imread('CheckerboardImage.png');

Load the camera parameters into the workspace.

intrinsic = load('calibration.mat');

Set the size of the checkerboard squares in millimeters.

squareSize = 200;

Estimate the checkerboard corners.

boardCorners = estimateCheckerboardCorners3d(Image, ...
    intrinsic.cameraParams,squareSize)

boardCorners = 4×3

    1.2840   -0.5216    8.8913
    2.8614    0.5774    8.3401
    1.8230    2.0470    8.2984
    0.2455    0.9480    8.8496

Plot the corners on the input image.

imPts = projectLidarPointsOnImage(boardCorners,intrinsic.cameraParams,rigid3d());
J = undistortImage(Image,intrinsic.cameraParams);
imshow(J)
hold on
plot(imPts(:,1),imPts(:,2),'.r','MarkerSize',30)
title('Detected Checkerboard Corners')
hold off

Input Arguments

I — Image for detection

H-by-W-by-C array

Image for detection, specified as an H-by-W-by-C array where:

• H – Height of the image in pixels

• W – Width of the image in pixels

• C – Number of color channels

Data Types: single | double | int16 | uint8 | uint16

imageFileNames — Image file names

character vector | cell array of character vectors

Image file names, specified as a character vector or cell array of character vectors If specifying more than one file name, you must use a cell array of character vectors.

Data Types: char | cell

imageArray — Set of images

H-by-W-by-C-by-N array

Set of images, specified as an H-by-W-by-C-by-N array where:

• H – Height of the tallest image in the array

• W – Width of the widest image in the array

• C – Number of color channels

• N – Number of images in the array

Data Types: single | double | int16 | uint8 | uint16

cameraIntrinsic — Camera intrinsic parameters

cameraIntrinsics object

Camera intrinsic parameters, specified as a cameraIntrinsics object.

checkerSize — Size of checkerboard square

scalar

Size of a checkerboard square, specified as a scalar in millimeters. This value specifies the length of each side of a checkerboard square.

Data Types: single | double

Name-Value Pair Arguments

Specify optional comma-separated pairs of Name,Value arguments. Name is the argument name and Value is the corresponding value. Name must appear inside quotes. You can specify several name and value pair arguments in any order as Name1,Value1,...,NameN,ValueN.

Example: 'MinCornerMetric',0.2 sets the threshold for the checkerboard corner metric to 0.2.

'Padding' — Padding along each side of checkerboard

[0 0 0 0] (default) | four-element row vector

Padding along each side of checkerboard, specified as the comma-separated pair consisting of 'Padding' and a four-element row vector of nonnegative values in millimeters.

The figure shows how the elements of the vector pad the sides.

Checkerboard Padding

Data Types: single | double

'MinCornerMetric' — Threshold for checkerboard corner metric

0.15 (default) | nonnegative scalar

Threshold for the checkerboard corner metric, specified as the comma-separated pair consisting of 'MinCornerMetric' and a nonnegative scalar. Using a higher threshold value can reduce the number of false detections in a noisy or highly textured image.

Data Types: single | double

'ShowProgressBar' — Display function progress

false (default) | true

Display function progress in a progress bar, specified as the comma-separated pair consisting of 'ShowProgressBar' and a logical false or true.

Data Types: logical

Output Arguments

imageCorners3d — Estimated location of checkerboard corners

4-by-3 matrix | 4-by-3-by-P array

Estimated location of checkerboard corners, returned as a 4-by-3 matrix or 4-by-3-by-P array. For one image, the function returns the 3-D world frame coordinates of the four checkerboard corners. Each row represents the x-, y- , z-axis coordinates of a corner point in meters. For multiple images, the coordinates are returned as a 4-by-3-by-P array, where P is the number of images in which a checkerboard was detected.

boardDimensions — Checkerboard dimensions

two-element row vector

Checkerboard dimensions, returned as a two-element row vector. The elements represent the width and length of the checkerboard respectively, in millimeters. The dimensions of the checkerboard are expressed in terms of the number of squares. The function calculates the dimensions of the checkerboard by multiplying the size of the checkerboard squares, checkerSize, by the number of detected squares along a side.

imagesUsed — Pattern detection flag

N-by-1 logical array

Pattern detection flag, returned as an N-by-1 logical array. N is the number of images in the first input argument. A value of 1 (true) indicates that the function detected a checkerboard pattern in the corresponding image. A value of 0 (false) indicates that the function did not detect a checkerboard pattern in the corresponding image.