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Parabolic lane boundary model


The parabolicLaneBoundary object contains information about a parabolic lane boundary model.


To generate parabolic lane boundary models that fit a set of boundary points and an approximate width, use the findParabolicLaneBoundaries function. If you already know your parabolic parameters, create lane boundary models by using the parabolicLaneBoundary function (described here).



boundaries = parabolicLaneBoundary(parabolicParameters) creates an array of parabolic lane boundary models from an array of [A B C] parameters for the parabolic equation y = Ax2 + Bx + C. Points within the lane boundary models are in world coordinates.

Input Arguments

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Coefficients for parabolic models of the form y = Ax2 + Bx + C, specified as an [A B C] real-valued vector or as a matrix of [A B C] values. Each row of parabolicParameters describes a separate parabolic lane boundary model.


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Coefficients for a parabolic model of the form y = Ax2 + Bx + C, specified as a real-valued vector of the form [A B C].

Type of lane boundary, specified as a LaneBoundaryType enumeration. Supported lane boundary types are:

  • Unmarked

  • Solid

  • Dashed

  • BottsDots

  • DoubleSolid

Lane boundary objects always return BoundaryType as type Solid. Update these types to match the types of the lanes that are being fitted. To update a lane boundary type, use the LaneBoundaryType.BoundaryType syntax. For example, this code sample shows how to update the first output lane boundary to type BottsDots:

boundaries(1) = LaneBoundaryType.BottsDots;

Strength of the boundary model, specified as a real scalar. Strength is the ratio of the number of unique x-axis locations on the boundary to the length of the boundary specified by the XExtent property. A solid line without any breaks has a higher strength than a dotted line that has breaks along the full length of the boundary.

Length of the boundary along the x-axis, specified as a real-valued vector of the form [minX maxX] that describes the minimum and maximum x-axis locations.

Object Functions

computeBoundaryModelObtain y-coordinates of lane boundaries given x-coordinates


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Create left-lane and right-lane parabolic boundary models.

llane = parabolicLaneBoundary([-0.001 0.01  0.5]);
rlane = parabolicLaneBoundary([-0.001 0.01 -0.5]);

Create a bird's-eye plot and lane boundary plotter. Plot the lane boundaries.

bep = birdsEyePlot('XLimits',[0 30],'YLimits',[-5 5]);
lbPlotter = laneBoundaryPlotter(bep,'DisplayName','Lane boundaries');
plotLaneBoundary(lbPlotter, [llane rlane]);

Find lanes in an image by using parabolic lane boundary models. Overlay the identified lanes on the original image and on a bird's-eye-view transformation of the image.

Load an image of a road with lanes. The image was obtained from a camera sensor mounted on the front of a vehicle.

I = imread('road.png');

Transform the image into a bird's-eye-view image by using a preconfigured sensor object. This object models the sensor that captured the original image.

bevSensor = load('birdsEyeConfig');
birdsEyeImage = transformImage(bevSensor.birdsEyeConfig,I);

Set the approximate lane marker width in world units (meters).

approxBoundaryWidth = 0.25;

Detect lane features and display them as a black-and-white image.

birdsEyeBW = segmentLaneMarkerRidge(im2gray(birdsEyeImage), ...

Obtain the image coordinates corresponding to the lane candidate positions. The find function returns pixel indices that correspond to the candidate lane positions. By convention, the order of the image coordinates is always reversed relative to the pixel indices. For more information about image coordinates, see Coordinate Systems.

Obtain the corresponding lane boundary points in vehicle coordinates by using the imageToVehicle function.

[imageY,imageX] = find(birdsEyeBW);
xyBoundaryPoints = imageToVehicle(bevSensor.birdsEyeConfig,[imageX,imageY]);

Find lane boundaries in the image by using the findParabolicLaneBoundaries function. By default, the function returns a maximum of two lane boundaries. The boundaries are stored in an array of parabolicLaneBoundary objects.

boundaries = findParabolicLaneBoundaries(xyBoundaryPoints,approxBoundaryWidth);

Use insertLaneBoundary to overlay the lanes on the original image. The XPoints vector represents the lane points, in meters, that are within range of the ego vehicle's sensor. Specify the lanes in different colors. By default, lanes are yellow.

XPoints = 3:30;

sensor = bevSensor.birdsEyeConfig.Sensor;
lanesI = insertLaneBoundary(I,boundaries(1),sensor,XPoints);
lanesI = insertLaneBoundary(lanesI,boundaries(2),sensor,XPoints,'Color','green');

View the lanes in the bird's-eye-view image.

BEconfig = bevSensor.birdsEyeConfig;
lanesBEI = insertLaneBoundary(birdsEyeImage,boundaries(1),BEconfig,XPoints);
lanesBEI = insertLaneBoundary(lanesBEI,boundaries(2),BEconfig,XPoints,'Color','green');

Extended Capabilities

Version History

Introduced in R2017a