Getting to camera coordinates from world coordinates. (estimateC​ameraParam​eters)

I did a camera calibration, which gives me the cameraParams . I then assumed that I could do

A          = cameraParams.PatternExtrinsics(2).A; % I'm interested in the second image
A(:,4)     = A(:,4)/1000; % If I dont do in meters, things look terrible. 
K          = cameraParams.K
WorldPoints      = cameraParams.WorldPoints'/1000;
WorldPoints(3,:) = 0; % need a z coordinate for the world points
WorldPoints(4,:) = 1; % need a 4th row, with a one, as according to the 'algorithms' section here: https://nl.mathworks.com/help/vision/ref/estimatecameraparameters.html, what we want to do is impoints=KA[X Y Z 1]'

tmp1             = A*WorldPoints; % need to do this step first, otherwise cannot multiply with camera params
imagePoints      = K*tmp1(1:3,:); 
imagePoints      = imagePoints(1:2,:);%this should be equal to the image coordinates?
realimagePoints  = cameraParams.ReprojectedPoints(:,:,2)';% but it's not equal to this

However, the thus obtained imagePoints does not equal realimagePoints(which does agree with the image that I have of the checkerboard that I used). Why is that? And how would I be able to get from the WorldPoints to imagePoints? As far as I understand, this should be possible given the info in cameraParams??

Answer 1

[Sjoerd]

Got it. All I needed to do was;

imagePoints(1,:) =imagePoints(1,:)./imagePoints(3,:);

imagePoints(2,:) =imagePoints(2,:)./imagePoints(3,:);