Transform image to bird's-eye view
Create a bird's-eye-view image from an image obtained by a front-facing camera mounted on a vehicle. Display points within the bird's-eye view using the vehicle and image coordinate systems.
Define the camera intrinsics and create an object containing these intrinsics.
focalLength = [309.4362 344.2161]; principalPoint = [318.9034 257.5352]; imageSize = [480 640]; camIntrinsics = cameraIntrinsics(focalLength,principalPoint,imageSize);
Set the height of the camera to be about 2 meters above the ground. Set the pitch of the camera to 14 degrees toward the ground.
height = 2.1798; pitch = 14;
Create an object containing the camera configuration.
sensor = monoCamera(camIntrinsics,height,'Pitch',pitch);
Define the area in front of the camera that you want to transform into a bird's-eye view. Set an area from 3 to 30 meters in front of the camera, with 6 meters to either side of the camera.
distAhead = 30; spaceToOneSide = 6; bottomOffset = 3; outView = [bottomOffset,distAhead,-spaceToOneSide,spaceToOneSide];
Set the output image width to 250 pixels. Compute the output length automatically from the width by setting the length to
outImageSize = [NaN,250];
Create an object for performing bird's-eye-view transforms, using the previously defined parameters.
birdsEye = birdsEyeView(sensor,outView,outImageSize);
Load an image that was captured by the sensor.
I = imread('road.png'); figure imshow(I) title('Original Image')
Transform the input image into a bird's-eye-view image.
BEV = transformImage(birdsEye,I);
In the bird's-eye-view image, place a 20-meter marker directly in front of the sensor. Use the
vehicleToImage function to specify the location of the marker in vehicle coordinates. Display the marker on the bird's-eye-view image.
imagePoint = vehicleToImage(birdsEye,[20 0]); annotatedBEV = insertMarker(BEV,imagePoint); annotatedBEV = insertText(annotatedBEV,imagePoint + 5,'20 meters'); figure imshow(annotatedBEV) title('Bird''s-Eye-View Image: vehicleToImage')
Define a location in the original bird's-eye-view image, this time in image coordinates. Use the
imageToVehicle function to convert the image coordinates to vehicle coordinates. Display the distance between the marker and the front of the vehicle.
imagePoint2 = [120 400]; annotatedBEV = insertMarker(BEV,imagePoint2); vehiclePoint = imageToVehicle(birdsEye,imagePoint2); xAhead = vehiclePoint(1); displayText = sprintf('%.2f meters',xAhead); annotatedBEV = insertText(annotatedBEV,imagePoint2 + 5,displayText); figure imshow(annotatedBEV) title('Bird''s-Eye-View Image: imageToVehicle')
birdsEye— Object for transforming image to bird's-eye view
Object for transforming image to bird's-eye view, specified as a
I— Input image
Input image, specified as a truecolor or grayscale image. The
OutputView property of
birdsEye determines the portion of
I to transform to a bird's-eye view.
I must not contain lens distortion. You can remove
lens distortion by using the
undistortImage (Computer Vision Toolbox) function. In
high-end optics, you can ignore distortion.