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Import Camera Intrinsic Parameters from ROS

The ROS camera calibration package estimates camera intrinsic parameters using the OpenCV camera calibration tools [1]. After calibrating a camera in ROS, you can import its intrinsic parameters to a YAML file using the camera calibration parser in ROS. To use the calibrated camera with Computer Vision Toolbox™ functions, such as undistortImage, you must read the camera parameters from the YAML file and then convert them into a cameraIntrinsics object using cameraIntrinsicsFromOpenCV.

Note: The cameraIntrinsicsFromOpenCV function supports importing camera intrinsic parameters for only those pinhole camera models that use the ROS plumb-bob distortion model.

Read Camera Intrinsic Parameters from a ROS YAML File

Read the camera parameters stored in cameraParams.yaml using the helper function helperReadYAML.

intrinsicsParams = helperReadYAML('cameraParams.yaml');

Create cameraIntrinsics Object Using cameraIntrinsicsFromOpenCV

Use the cameraIntrinsicsFromOpenCV function to create a cameraIntrinsics object from the camera matrix and the distortion coefficients.

imageSize = [intrinsicsParams.image_height intrinsicsParams.image_width];
intrinsicMatrix = intrinsicsParams.camera_matrix;
distortionCoefficients = intrinsicsParams.distortion_coefficients;

intrinsicsObj = cameraIntrinsicsFromOpenCV(intrinsicMatrix,distortionCoefficients,imageSize);

Undistort Image

Use the imported camera intrinsics with undistortImage to undistort an image captured using the calibrated camera.

% Load the captured image.
imageName = fullfile(toolboxdir('vision'),'visiondata','calibration','stereo','left','left01.png');
I = imread(imageName);

% Undistort the image.
J = undistortImage(I,intrinsicsObj,'OutputView','full');

% Display the result.

Figure contains an axes object. The axes object contains an object of type image.

Supporting Functions


The helperReadYAML function reads the monocular camera parameters from the input YAML file that was exported from ROS.

function cameraParams = helperReadYAML(filename)
% helperReadYAML reads a ROS YAML file, filename, and returns a structure 
% with these fields: image_width, image_height, camera_name,
% camera_matrix, distortion_model, distortion_coefficients,
% rectification_matrix, and projection_matrix. These fields are stored 
% in the YAML file colon separated from their values in different lines.

    f = fopen(filename,'r');
    stringFields = {'camera_name','distortion_model'};
    while ~feof(f)

        [name,value,isEmptyLine] = helperReadYAMLLine(f);
        if isEmptyLine

        if ~isempty(value)
            % Convert all values to numbers except for known string
            % fields.
            if ~any(contains(name, stringFields))
                value = str2num(value); %#ok
            % An empty value in ROS YAML files indicates a matrix in
            % upcoming lines. Read the matrix from the upcoming lines.
            value = helperReadYAMLMatrix(f);

        % Store post-processed value.
        cameraParams.(name) = value;


The helperReadYAMLMatrix function reads the rows, columns and data fields of a matrix in the ROS YAML file.

function matrix = helperReadYAMLMatrix(f)
%   helperReadYAMLMatrix reads a matrix from the ROS YAML file. A matrix in
%   a ROS YAML file has three fields: rows, columns and data. rows and col
%   describe the matrix size. data is a continguous array of the matrix
%   elements in row-major order. This helper function assumes the presence
%   of all three fields of a matrix to return the correct matrix.

    numRows = 0;
    numCols = 0;
    data = [];

    % Read numRows, numCols and matrix data.
    while ~feof(f)
        [name,value,isEmptyLine] = helperReadYAMLLine(f);

        if isEmptyLine

        switch name
            case 'rows'
                numRows = str2num(value); %#ok
            case 'cols'
                numCols = str2num(value); %#ok
            case 'data'
                data    = str2num(value); %#ok

                % Terminate the while loop as data is the last 
                % field of a matrix in the ROS YAML file.
                % Terminate the while loop if any other field is
                % encountered.

    if numel(data) == numRows*numCols
        % Reshape the matrix using row-major order.
        matrix = reshape(data,[numCols numRows])';


The helperReadYAMLLine function reads a line of a ROS YAML file.

function [name,value,isEmptyLine] = helperReadYAMLLine(f)

    % Read line from file.
    line = fgetl(f); 

    % Trim leading and trailing whitespaces.
    line = strtrim(line);

    if isempty(line) || line(1)=='#'
        % Empty line or comment.
        name = '';
        value = '';
        isEmptyLine = true;
        % Split the line to get name and value.
        c = strsplit(line,':');
        assert(length(c)==2,'Unexpected file format')
        name = c{1};
        value = strtrim(c{2}); % Trim leading whitespace.
        isEmptyLine = false;