校准图像以获得位于同一平面上的点的俯视图

校准:

我在Matlab中使用这个视觉工具箱校准了相机.我使用棋盘图像来做到这一点.校准后,我得到cameraParams,其中包含:

Camera Extrinsics
RotationMatrices: [3x3x18 double]
TranslationVectors: [18x3 double]

和

 Camera Intrinsics
 IntrinsicMatrix: [3x3 double]
 FocalLength: [1.0446e+03 1.0428e+03]
 PrincipalPoint: [604.1474 359.7477]
 Skew: 3.5436

目的: 我使用这台相机记录了一些运动物体的轨迹.每个对象对应于帧中的单个点.现在,我想要投射点,以便我得到一个顶视图.

请注意我希望转换的所有这些点都在同一个平面上.

例如:[xcor_i,ycor_i]

-101.7000  -77.4040
-102.4200  -77.4040

关键点:此平面垂直于用于校准的棋盘图像之一.对于那张图片(下图),我知道棋盘的起点高度(193.040厘米).投影点的平面与地面平行并垂直于该图像.

代码 (参考:https://stackoverflow.com/a/27260492/3646408并在下面以@Dima回答):

function generate_homographic_matrix()
%% Calibrate camera
% Define images to process
path=['.' filesep 'Images' filesep];
list_imgs=dir([path '*.jpg']);
list_imgs_path=strcat(path,{list_imgs.name});

% Detect checkerboards in images
[imagePoints, boardSize, imagesUsed] = detectCheckerboardPoints(list_imgs_path);
imageFileNames = list_imgs_path(imagesUsed);

% Generate world coordinates of the corners of the squares
squareSize = 27;  % in units of 'mm'
worldPoints = generateCheckerboardPoints(boardSize, squareSize);

% Calibrate the camera
[cameraParams, imagesUsed, estimationErrors] = estimateCameraParameters(imagePoints, worldPoints, ...
    'EstimateSkew', true, 'EstimateTangentialDistortion', true, ...
    'NumRadialDistortionCoefficients', 3, 'WorldUnits', 'mm');
%% Compute homography for peripendicular plane to checkerboard
% Detect the checkerboard 
im=imread(['.' filesep 'Images' filesep 'exp_19.jpg']); %exp_19.jpg is the checkerboard orthogonal to the floor
[imagePoints, boardSize] = detectCheckerboardPoints(im);

% Compute rotation and translation of the camera.
[Rc, Tc] = extrinsics(imagePoints, worldPoints, cameraParams);

% Rc(rotation of the calibration view w.r.t the camera) = [x y z])
%then the floor has rotation Rf = [z x -y].(Normal vector of the floor goes up.)
Rf=[Rc(:,3),Rc(:,1),Rc(:,2)*-1];

% Translate it to the floor
H=452;%distance btw origin and floor
Fc = Rc * [0; H; 0];
Tc = Tc + Fc';

% Combine rotation and translation into one matrix:
Rf(3, :) = Tc;

% Compute the homography between the checkerboard and the image plane:
H = Rf * cameraParams.IntrinsicMatrix;

save('homographic_matrix.mat','H')
end

%% Transform points
function [x_transf,y_transf] =transform_points(xcor_i,ycor_i)
% creates a projective2D object and then transforms the points forward to
% get a top-view
% xcor_i and ycor_i are 1d vectors comprising of the x-coordinates and
% y-coordinates of trajectories. 
data=load('homographic_matrix.mat');
homo_matrix=data.H;
tform=projective2d(inv(homo_matrix));
[x_transf,y_transf] = transformPointsForward(tform,xcor_i,ycor_i);
end

从OReilly Learning OpenCV Pg 412引用文本:"一旦我们按照我们的意愿设置单应矩阵和高度参数,我们就可以移除棋盘并推动推车,制作路径的鸟瞰视频...... "这就是我基本上希望实现的目标.