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Convert vehicle coordinates to bird's-eye-view image coordinates



imagePoints = vehicleToImage(birdsEye,vehiclePoints) converts vehicle coordinates to [x y] bird’s-eye-view image coordinates.


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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 NaN.

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');
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');

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);

title('Bird''s-Eye-View Image: imageToVehicle')

Input Arguments

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Object for transforming image to bird's-eye view, specified as a birdsEyeView object.

Vehicle points, specified as an M-by-2 matrix containing M number of [x y] vehicle coordinates.

Output Arguments

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Image points, returned as an M-by-2 matrix containing M number of [x y] image coordinates.

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using MATLAB® Coder™.

Version History

Introduced in R2017a