Why does transforming with affine3D yield different result than multiplying with transfomation matrix?

Question

Jorrit Goddijn 2018-8-6

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/413799-why-does-transforming-with-affine3d-yield-different-result-than-multiplying-with-transfomation-matri

回答： Lewis Newton 2020-2-27

在 MATLAB Online 中打开

Hi,

I am trying to transform a pointcloud with a transformation matrix on a point-per-point basis.

In the following script I run a pctransform which does indeed shift the pointcloud over a unit of 1.

However, when applying the same transformation matrix on a point per point basis, I dont see any difference in the resulting point cloud.

I cant use pctransform in my final setup since my transformation matrices are non-rigid.

Could anyone point me out what i am doing wrong?

ptCloud1 = pointCloud(rand(10000,3,'single'));
moveRight = [1 0 0 0; ...
             0 1 0 0; ...
             0 0 1 0; ...
             1 0 0 1];
ptCloudRight = pctransform(copy(ptCloud1),affine3d(moveRight));
pcshowpair(ptCloud1,ptCloudRight);
ptCloudRightCreated = pointCloud(transformPoints(copy(ptCloud1), moveRight))
pcshowpair(ptCloud1,ptCloudRightCreated);
function newPoints = transformPoints(ptc, tmatrix)
newPoints = [];
disp(tmatrix)
for i = 1 : ptc.Count
    point = [ptc.Location(i,:), 0];
    tPoint = point * tmatrix;
    newPoints = cat(1, newPoints, tPoint(1:3));
end
end

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Answer 1

Kin Sung Chan 2019-11-9

0
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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/413799-why-does-transforming-with-affine3d-yield-different-result-than-multiplying-with-transfomation-matri#answer_400629

在 MATLAB Online 中打开

ptCloud = pointCloud(rand(10000,3,'single'));
moveRight = [1 0 0 0; ...
             0 1 0 0; ...
             0 0 1 0; ...
             1 0 0 1];
         
tform = affine3d(moveRight);
ptCloudRight  = pctransform(ptCloud, tform);
figure(1)
pcshowpair(ptCloud, ptCloudRight ); 