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estimateMonoCameraFromScene

Estimate monocular camera parameters from scene geometry

    Description

    example

    [pitch,yaw,roll,height,intrinsicsOut] = estimateMonoCameraFromScene(trapezoid,rectangleWidth,rectangleLength,imageSize) estimates the extrinsic and intrinsic parameters of a monocular camera from scene geometry. Specify the pixel coordinates for a trapezoid on the scene image, along with the width and length of the real-world rectangle that corresponds to that trapezoid. The returned extrinsic parameters define the pitch, yaw, and roll rotation angles between the camera coordinate system and vehicle coordinate system axes. The function also returns the height of the camera above the ground, and the intrinsic parameters of the camera intrinsicsOut. Use these estimates to configure a monoCamera object when a formal calibration with a calibration pattern is not possible. For more information on coordinate systems see, camera coordinate system and vehicle coordinate system.

    Image showing how trapezoid vertices in image coordinates relate to the width and length of the corresponding real-world rectangle.

    example

    [pitch,yaw,roll,height,intrinsicsOut] = estimateMonoCameraFromScene(trapezoid,rectangleWidth,intrinsicsIn) specifies the intrinsic parameters of the camera intrinsicsIn instead of the rectangle length and image size. When the camera intrinsic parameters are available, use this syntax to improve the estimates of the extrinsic parameters.

    Examples

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    Load a MAT file containing a scene image into the workspace.

    load("doubleLaneImageData.mat");

    Specify the pixel coordinates of trapezoid vertices on the scene image that spans the width of two lanes. You must specify the vertices, in the clockwise or counterclockwise order, starting from the upper-left trapezoid vertex.

    trapezoid = [208 456; 170 465; 699 467; 693 456];

    Visualize the trapezoid vertices as annotations on the scene image. Note that the vertices in counterclockwise order.

    doubleLaneImg = insertMarker(doubleLaneImg,trapezoid);
    text_str = {'UL','LL','LR','UR'};
    doubleLaneImg = insertText(doubleLaneImg,trapezoid+[5 5; 5 5; 5 5; 5 -25],text_str);
    figure
    imshow(doubleLaneImg)

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

    Specify the dimensions of the real-world rectangle that corresponds to the trapezoid on the scene image.

    rectangleWidth = 8;
    rectangleLength = 1.5;

    Specify the size of the image.

    imageSize = size(doubleLaneImg,[1 2]);

    Estimate the extrinsic and intrisic camera parameters by using the estimateMonoCameraFromScene function. Display the estimated camera extrinsic and intrinsic parameters.

    [pitch,yaw,roll,height,intrinsics] = estimateMonoCameraFromScene(trapezoid,rectangleWidth,rectangleLength,imageSize)
    pitch = 0.3032
    
    yaw = -0.1190
    
    roll = 2.0457
    
    height = 1.4508
    
    intrinsics = 
      cameraIntrinsics with properties:
    
                 FocalLength: [1.0981e+03 1.0981e+03]
              PrincipalPoint: [640 360]
                   ImageSize: [720 1280]
            RadialDistortion: [0 0]
        TangentialDistortion: [0 0]
                        Skew: 0
                           K: [3x3 double]
    
    

    Obtain camera extrinsic parameters by specifying the scene geometry interactively on an image when camera intrinsic parameters are available. Then, use the estimated camera parameters to create a monoCamera object, and obtain a bird's-eye-view of the scene by using a birdsEyeView object.

    Obtain Camera Parameters

    Load the scene image. Use the known camera intrinsic parameters to create a cameraIntrinsics object.

    Im = imread(fullfile(matlabroot, "toolbox", "driving", "drivingdata", "roadSequence", "f00014.png"));
    
    focalLength = [309.4362 344.2161];
    principalPoint = [318.9034 257.5352];
    imageSize = [480 640];
    intrinsics = cameraIntrinsics(focalLength,principalPoint,imageSize);

    Display the scene image. Move the four vertices of the trapezoid region of interest (ROI) interactively to specify the desired scene geometry. Then press Enter.

    figure
    imshow(Im);
    title("Adjust the trapezoid ROI to select rectangular lane region, press Enter to continue");
    vertices = [size(Im,2)/2 size(Im,1)/2;...
                size(Im,2)/2 size(Im,1)*3/4;...
                size(Im,2)*3/4 size(Im,1)*3/4;...
                size(Im,2)*3/4 size(Im,1)/2];
    roi = drawpolygon(Position=vertices,FaceAlpha=0.2,LineWidth=1);
    
    % Wait until Enter is pressed
    wasButtonPressed = false;
    while ~wasButtonPressed
        wasButtonPressed = waitforbuttonpress;
        if double(get(gcf,"currentcharacter")) ~= 13
            wasButtonPressed = false;
        end
    end

    {"String":"Figure contains an axes object. The axes object with title Adjust the trapezoid ROI to select rectangular lane region, press Enter to continue contains 2 objects of type image, images.roi.polygon.","Tex":"Adjust the trapezoid ROI to select rectangular lane region, press Enter to continue","LaTex":[]}

    Specify the dimensions of the real-world rectangle that corresponds to the trapezoid you specified on the scene image. Because you know the camera intrinsic parameters, you can estimate the extrinsic parameters by specifying only the width of the rectangle.

    rectangleWidth = 3.6;

    Estimate the camera extrinsic parameters to obtain the pitch, roll, yaw, and height of the camera mounted on the vehicle.

    [pitchCal,yawCal,rollCal,heightCal] = estimateMonoCameraFromScene(roi.Position,rectangleWidth,intrinsics);

    Transform Road Image to Bird's-Eye-View Image

    Create a monoCamera object using the estimated camera extrinsic parameters and the known intrinsic parameters.

    sensor = monoCamera(intrinsics,heightCal,Pitch=pitchCal,Roll=rollCal,Yaw=yawCal);

    Define the area in front of the camera that you want to transform into a bird's-eye view. Specify an area from 3 to 30 meters in front of the camera, with 6 meters to either side of the camera.

    distAhead = 40;
    spaceToOneSide = 6;
    bottomOffset = 3;
    outView = [bottomOffset distAhead -spaceToOneSide spaceToOneSide];

    Set the output image width to 250 pixels. Compute the output height automatically from the width by specifying the length as NaN.

    outImageSize = [NaN 250];

    Create a birdsEyeView object using the previously defined parameters, and transform the road image. Visualize the bird's-eye-view image.

    birdsEye = birdsEyeView(sensor,outView,outImageSize);
    BEV = transformImage(birdsEye,Im);
    imshow(BEV)

    {"String":"Figure contains an axes object. The axes object contains an object of type image.","Tex":[],"LaTex":[]}

    Input Arguments

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    Vertices of a trapezoid on the scene image, in pixel coordinates, specified as a 4-by-2 array. Each row specifies the position of a vertex, and you start with the upper-left vertex of the trapezoid and must follow either clockwise or counterclockwise order.

    Data Types: single | double

    Width of the real-world rectangle that corresponds to the trapezoid on the scene image, in meters, specified as a positive scalar.

    Data Types: single | double

    Length of the real-world rectangle that corresponds to the trapezoid on the scene image, in meters, specified as a positive scalar.

    Data Types: single | double

    Size of the image, in pixels, specified as a two-element vector of the form [m n], where m and n specify the number of rows and columns of pixels, respectively.

    Data Types: single | double

    Intrinsic camera parameters, specified as a cameraIntrinsics object.

    Output Arguments

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    Pitch angle between the horizontal plane of the vehicle and the optical axis of the camera, returned as a real scalar in degrees. pitch uses the ISO convention for rotation, with a clockwise-positive angle direction when looking in the positive direction of the vehicle's YV-axis.

    Side-by-side images of a camera with the Xv, Yv, and Zv axes labeled. In the first image, the camera is straight. In the second image, the camera is tilted down to indicate a change in pitch angle.

    For more details, see Angle Directions.

    Yaw angle between the XV-axis of the vehicle and the optical axis of the camera, returned as a real scalar in degrees. yaw uses the ISO convention for rotation, with a clockwise-positive angle direction when looking in the positive direction of the vehicle's ZV-axis.

    Side-by-side images of a camera with the Xv, Yv, and Zv axes labeled. In the first image, the camera is facing forward. In the second image, the camera is rotated to the left to indicate a change in yaw angle.

    For more details, see Angle Directions.

    Roll angle of the camera around its optical axis, returned as a real scalar in degrees. roll uses the ISO convention for rotation, with a clockwise-positive angle direction when looking in the positive direction of the vehicle's XV-axis.

    Side-by-side images of a camera with the Xv, Yv, and Zv axes labeled. In the first image, the camera is straight. In the second image, the camera is rotated around its axis to indicate a change in pitch angle.

    For more details, see Angle Directions.

    Perpendicular height from the ground to the focal point of the camera, returned as a nonnegative real scalar in meters.

    Vehicle with front-facing camera on its hood, and the camera height above the ground marked

    Intrinsic camera parameters, returned as a cameraIntrinsics object.

    Limitations

    • The cameraIntrinsics object returned has the same estimated focal length values in x and y.

    • The function does not estimate skew, radial distortion, and tangential distortion. These values are 0 in the returned cameraIntrinsics object.

    Version History

    Introduced in R2022b