projectLidarPointsOnImage

R2026b

Project lidar points onto an image frame

Syntax

imPts = projectLidarPointsOnImage(ptCloudIn,intrinsics,tform)

imPts = projectLidarPointsOnImage(worldPoints,intrinsics,tform)

[imPts,indices] = projectLidarPointsOnImage(___)

[___] = projectLidarPointsOnImage(___,Name,Value)

Description

imPts = projectLidarPointsOnImage(ptCloudIn,intrinsics,tform) projects lidar point cloud data onto an undistorted image using a rigid transformation between the lidar sensor and camera, tform, and a set of camera intrinsic parameters that correspond to the undistorted image, intrinsics. The output imPts contains the 2-D coordinates of the projected points on the udistorted image.

imPts = projectLidarPointsOnImage(worldPoints,intrinsics,tform) projects lidar points, specified as 3-D coordinates in the world frame, onto the undistorted image.

[imPts,indices] = projectLidarPointsOnImage(___) returns the linear indices of the projected points in the point cloud using any combination of input arguments in previous syntaxes.

[___] = projectLidarPointsOnImage(___,Name,Value) specifies options using one or more name-value arguments in addition to any combination of arguments in previous syntaxes. For example, 'ImageSize',[250 400] sets the size of the image on which to project the points to 250-by-400 pixels.

Examples

Overlay Projected Lidar Points on Image

Load a MAT file containing a synchronized image and point cloud pair, the camera intrinsics and the lidar to camera transformation.

ld  = load("sampleColoredPtCloud.mat");

Extract the image and point cloud data.

I = ld.I;
ptCloud = ld.ptCloud;

Downsample the point cloud data.

ptCloud = pcdownsample(ptCloud,"gridNearest",0.5);

Visualize the image and point cloud data.

figure
subplot(1,2,1)
imshow(I)
title("Image")

subplot(1,2,2)
pcshow(ptCloud)
title("Point Cloud")

Get the camera intrinsics and the transformation from the lidar sensor to the camera.

intrinsics = ld.intrinsics;
lidarToCameraTform = ld.lidarToCameraTform;

Project the point cloud into the image.

imPts = projectLidarPointsOnImage(ptCloud,intrinsics,lidarToCameraTform);

Overlay the projected points on the image.

figure
imshow(I)
hold on
plot(imPts(:,1),imPts(:,2),".")

Input Arguments

ptCloudIn — Point cloud

pointCloud object

Point cloud, specified as a pointCloud object.

worldPoints — Points in world coordinate frame

M-by-3 matrix | M-by-N-by-3 array

Points in the world coordinate frame, specified as an M-by-3 matrix or M-by-N-by-3 array. If you specify an M-by-3 matrix, each row contains 3-D world coordinates of a point in an unorganized point cloud that contains M points in total. If you specify an M-by-N-by-3 array, M and N represent the number of rows and columns, respectively, in an organized point cloud. Each channel of the array contains the 3-D world coordinates of that point.

Data Types: single | double

intrinsics — Camera intrinsic parameters corresponding to the undistorted image

cameraIntrinsics object

Camera intrinsic parameters corresponding to the undistorted image, specified as a cameraIntrinsics (Computer Vision Toolbox) object. You can obtain the camera intrinsics using the undistortImage (Computer Vision Toolbox) function to undistort the image.

tform — Lidar to camera rigid transformation

rigidtform3d object

Lidar to camera rigid transformation, specified as a rigidtform3d (Image Processing Toolbox) object.

Name-Value Arguments

Specify optional pairs of arguments as Name1=Value1,...,NameN=ValueN, where Name is the argument name and Value is the corresponding value. Name-value arguments must appear after other arguments, but the order of the pairs does not matter.

Example: ImageSize=[250 400] sets the size of the image on which to project the points to 250-by-400 pixels.

Before R2021a, use commas to separate each name and value, and enclose Name in quotes.

Example: 'ImageSize',[250 400] sets the size of the image on which to project the points to 250-by-400 pixels.

Indices — Indices selected for projection onto image coordinate frame

vector of positive integers

Indices selected for projection onto image coordinate frame, specified as a vector of positive integers.

Data Types: single | double

ImageSize — Size of image on which points are projected

intrinsics.ImageSize (default) | two-element row vector

Size of the image on which the points are projected, specified as a two-element row vector of the form [width height] in pixels. The function uses the specified dimensions to filter out the projected points that are not in the field of view of the camera.

If you do no specify the 'ImageSize' argument, then the function uses the ImageSize property from the camera intrinsic parameters intrinsics to estimate the field of view of the camera.

Note

If you specify an 'ImageSize' argument greater than the default argument, then the function uses the default argument.

Data Types: single | double

Output Arguments

imPts — Points projected on image

M-by-2 matrix

Points projected onto the undistorted image, returned as an M-by-2 matrix. Each row contains the 2-D coordinates, in the form [x y], a point in the undistorted image.

Data Types: single | double

indices — Linear indices of projected points

vector of positive integers

Linear indices of the projected points of the point cloud, returned as a vector of positive integers.

Data Types: single | double

Extended Capabilities

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

GPU Code Generation
Generate CUDA® code for NVIDIA® GPUs using GPU Coder™.

Version History

Introduced in R2020b

R2022b: Supports rigidtform3d objects

You can now specify tform as a rigidtform3d (Image Processing Toolbox) object, which uses the premultiply convention. Although you can still specify tform as a rigid3d (Image Processing Toolbox) object, this object is not recommended because it uses the postmultiply convention. For more information, see Migrate Geometric Transformations to Premultiply Convention (Image Processing Toolbox).