multiCameraParameters

Store multi-camera system parameters

Since R2025a

Description

The multiCameraParameters object stores the intrinsic and extrinsic parameters of a multi-camera system estimated during multi-camera calibration.

Creation

Create a multiCameraParameters object using the estimateMultiCameraParameters function.

Properties

Extrinsic Parameters

CameraPoses — Pose of each camera relative to origin camera

Read-only: numCameras-element vector of rigidtform3d objects

This property is read-only.

Pose of each camera relative to the origin camera ReferenceCameraIndex, specified as a numCameras-element vector of rigidtform3d objects. numCameras represents the number of cameras.

ReferenceCameraIndex — Index of origin camera

Read-only: integer

This property is read-only.

Index of the origin camera, specified as an integer. This camera defines the reference coordinate system, and all other camera poses are defined relative to this reference camera. The pose of the reference camera is represented as rigidtform3d(eye(4)).

NumCameras — Number of cameras in system

integer

Number of cameras in the system, specified as an integer.

Intrinsic Parameters

Intrinsics — Intrinsic parameters for all cameras in multi-camera system

Read-only: numCameras-element cell array

This property is read-only.

Intrinsic parameters for all cameras in the multi-camera system, specified as a numCameras-element cell array containing cameraIntrinsics objects, fisheyeIntrinsics objects, or a combination of both. numCameras is the number of cameras.

Accuracy of Estimated Parameters

MeanReprojectionError — Average Euclidean distance

Read-only: scalar

This property is read-only.

Average Euclidean distance between reprojected points and detected points over all image pairs, specified as a scalar in pixels.

Data Types: double

MeanReprojectionErrorPerCamera — Average reprojection error for each camera

Read-only: numCameras-element vector

This property is read-only.

Average reprojection error for each camera, specified a numCameras-element vector. numCameras is the number of cameras.

MeanReprojectionErrorPerImage — Average reprojection error of each image

Read-only: numViews-by-numCameras vector

This property is read-only.

Average reprojection error of each image in pixels, specified as an numViews-by-numCameras vector.

MeanReprojectionErrorPerView — Average reprojection error of each view

Read-only: numViews-by-1 vector

This property is read-only.

Average reprojection error of each view in pixels, specified as an numViews-by-1 vector

ReprojectedPoints — World points reprojected onto calibration images

Read-only: numKeyPoints-by-2-by-numViews-by-numCameras-by-patternCount matrix

This property is read-only.

World points reprojected onto calibration images, specified as a numKeyPoints-by-2-by-numViews-by-numCameras-by-patternCount matrix.

Settings Used to Estimate Multi-Camera Parameters

PatternCount — Number of unique calibration patterns captured in calibration images

Read-only: scalar

This property is read-only.

Number of unique calibration patterns captured in the calibration images, specified as a scalar.

PatternPoses — Poses of calibration patterns relative to reference pattern

Read-only: P-element vector

This property is read-only.

Poses of calibration patterns relative to the reference pattern, specified as a P-element vector of rigidtform3d objects, where P represents the number of calibration patterns. The reference pattern is the first element of the PatternPoses vector, stored as PatternPoses(1). Subsequent elements represent the poses of other patterns relative to this reference pattern. The reference pattern's pose is given by rigidtform3d(eye(4)).

NumViews — Number of pattern views to estimate camera poses

Read-only: integer

This property is read-only.

Number of pattern views to estimate camera poses, specified as an integer.

CovisibilityMatrix — Covisibility of cameras

Read-only: numCameras-by-numCameras logical matrix

This property is read-only.

Covisibility of cameras based on the calibration images, specified as a numCameras-by-numCameras logical matrix. numCameras is the number of cameras.

WorldPoints — World coordinates of pattern keypoints

Read-only: numKeyPoints-by-2 matrix

This property is read-only.

World coordinates of pattern keypoints in the calibration pattern, specified as a numKeyPoints-by-2 matrix. numKeyPoints is the number of keypoints in the pattern.

WorldUnits — Units of world points

Read-only: "mm" (default) | character vector | string scalar

This property is read-only.

Units of world points, specified as a character vector or string scalar. This value describes the unit of measure.

Examples

Calibrate a Multi-Camera System using a ChArUco board

Estimate the relative position and orientation of six cameras with overlapping fields of view by using calibration images that contain a single ChArUco board.

Download the calibration images.

calibImagesURL = "https://www.mathworks.com/supportfiles/vision/data/overlapping-cameras-charuco.zip";
calibImagesDir = fullfile(pwd,"overlapping-cameras-charuco");
calibImagesZip = fullfile(pwd,"overlapping-cameras-charuco.zip");
if ~exist(calibImagesZip,"file")
    disp("Downloading calibration images (52 MB)...")
    websave(calibImagesZip,calibImagesURL);
end

Downloading calibration images (52 MB)...

if ~exist(calibImagesDir,"dir")
    unzip(calibImagesZip,pwd)
end

Specify calibration image filenames for each camera.

numCameras = 6;
camDirPrefix = "Cam00";
imageFiles = cell(1,numCameras);
for i = 1:numCameras
    camDir = fullfile(calibImagesDir,camDirPrefix+i);
    imds = imageDatastore(camDir);
    imageFiles{i} = imds.Files;
end
imageFiles = [imageFiles{:}];

Define the ChArUco board properties. Specify checker size and marker size in centimeters.

markerFamily = "DICT_6X6_1000";
patternDims = [5 5];
markerSize = 6.8;   % in cm
checkerSize = 9.15; % in cm
numKeyPoints = prod(patternDims - 1);
minMarkerId = 144;

Detect the key points of the ChArUco board in the calibration images.

imagePoints = detectPatternPoints(imageFiles,"charuco-board",patternDims, ...
    markerFamily,checkerSize,markerSize,MinMarkerID=minMarkerId);

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Generate the world points for the pattern.

worldPoints = patternWorldPoints("charuco-board",patternDims,checkerSize);

Load the intrinsic parameters of the six cameras. These parameters have been estimated using the Using the Single Camera Calibrator App.

ld = load("sixCameraIntrinsics.mat");

Perform multi-camera calibration.

params = estimateMultiCameraParameters(imagePoints,worldPoints,ld.intrinsics,WorldUnits="cm");

Visualize the calibration accuracy.

figure(Position=[100,100,1000,400])
showReprojectionErrors(params)

Visualize the camera extrinsic parameters.

figure
showExtrinsics(params)
view(2)

Version History

Introduced in R2025a

R2026a: New properties to support multiple calibration patternsPatternCount and PatternPoses properties

Added the PatternCount, PatternPoses MeanReprojectionErrorPerView, MeanReprojectionErrorPerImage, and ReprojectedPoints properties to support multiple calibration patterns.

R2026a: Computation of the MeanReprojectionError property has changed

The MeanReprojectionError property is computed as the mean of MeanReprojectionErrorPerImage over all images, omitting NaN values.