I am having a query in image transformation on fitgeotform2d function. Can anyone please explain what is moving points and fixed points and how to find them please?

I want to transform a narrow view image into a bied eye view projection on ADAS image. I selected the control points for the projection in this image. Please help me.

clear; close all
filename = 'C:\Users\dines\Downloads\43a.jpg';
img = im2double(rgb2gray(imread(filename)));
name = 'check2';
msgid = 'Images:initSize:adjustingMag';
warning('off',msgid);
imshow(img);
roadmarking=img;
[ xi , yi ] = getpts;
c = [ cpstruct.inputPoints(:,1) ]';
r = [cpstruct.inputPoints(:,2) ]';

base = [0 11; 11 11; 11 0; 0 0];
tf = fitgeotrans([c r],base*80,'projective');
disp('tf = ');
disp(tf)
T = tf.T;
disp('T =');
format short g
disp(T);

imshow(img);
hold on;
plot([c;c(1)],[r;r(1)],'r','Linewidth',2);
text(c(1),r(1)+20,'0, 11','Color','y');
text(c(2),r(2)+20,'11, 11','Color','y');
text(c(3),r(3)-20,'11, 0','Color','y');
text(c(4),r(4)-20,'0, 0','Color','y');
hold off;
F = getframe();
g = frame2im(F);
imwrite(g,[name '_overlay.jpg']);
[xf1, xf1_ref] = imwarp(img,tf);
imshow(xf1)
xf1_ref
imwrite(xf1,[name '_registered.jpg']);
bdi = [1 1; 1280 1; 1280 960; 1 960];
fill(bdi(:,1),bdi(:,2),'b');
axis ij;
hold on
fill(c,r,'r');
hold off
axis equal
% show the transformed simplified image
rd = transformPointsForward(tf,[c r]);
bds = transformPointsForward(tf,bdi);
fill(bds(:,1),bds(:,2),'b')
axis ij
hold on
fill(rd(:,1),rd(:,2),'r')
axis equal
hold off
% show that the control points map to the target points
prd = [c r ones(4,1)]*T;
% B = repmat(A,M,N) creates a large matrix B consisting of an M-by-N
%     tiling of copies of A.
%  This is used to produce two copies of the the third, homogeneous
%  variable. The end result is to convert homogeneous to normal variables.
uv = prd(:,1:2)./repmat(prd(:,3),1,2);
disp('uv/80 = ');
disp(uv/80)
xf1_ref.XWorldLimits = [-500 1500];
xf1_ref.YWorldLimits = [-800 1200];
xf1_ref.ImageSize = [2000 2000];
[xf2 xf2_ref] = imwarp(img,tf,'OutputView',xf1_ref);
xf2_ref
imshow(xf2)
imwrite(xf2,[name '_truncated.jpg']);
warning('on',msgid);

Answer 1

[Pratyush Swain]

Hi Dinesh,

I understand you want to create a bird's eye view projection of the given image.

Please go through the following implementation where i have leveraged 'fitgeotrans' function and 'imwarp' fucntion to create a transformed image:

% Load Image 
filename = '43a.jpg';
image = imread(filename);
% Define the source and destination points for the transformation
sourcePoints = [0,780;1920,780;1920,1080;0,1080];
destinationPoints = [0,0;1920,0;1920,1080;0,1080];
% Create a projective transformation object
tform = fitgeotrans(sourcePoints, destinationPoints, 'projective');
% Apply the transformation to the image
transformedImage = imwarp(image, tform);
% Display the original and transformed images
figure;
imshow(transformedImage);
title('Bird''s Eye View Image');

Please note 'fitgeotrans' is no longer recommended since R2022b release,you can use 'fitgeotform2d' function instead.

Hope this helps.