# why point correspondence to rotation matrix calculation is not my expected?

12 ビュー (過去 30 日間)
cui 2022 年 5 月 11 日
コメント済み: Matt J 2022 年 5 月 11 日
for example, at first ,one point P1(1,0,0) rotate pi/2 angle by y-axis,then get the point P2(0,0,-1), then rotate pi/2 angle by x-axis, then get the point P3(0,1,0). i use eul2rotm function to specify eular angle to get rotation matrix,then get the destination point by premultipy format,but get the result is not my expected P3?
P1 = [1,0,0];
eular = [0,pi/2,pi/2]
eular = 1×3
0 1.5708 1.5708
r = eul2rotm(eular,'ZYX'); % premultipy format
destinationPt = r*P1' % not same as P3 ?
destinationPt = 3×1
0.0000 0 -1.0000
if i take eular decompose into two component, ie rotate pi/2 angle correspondance to y-axis,x-axis, then i can get my expected result P3.
eularY = [0,pi/2,0];
eularX = [0,0,pi/2];
ry = eul2rotm(eularY);
rx = eul2rotm(eularX);
destiPt = rx*ry*P1' % is same as P3, which is my expect result.
destiPt = 3×1
0.0000 1.0000 -0.0000
i don't understand why eular angles vector three components not write together?

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### 採用された回答

Matt J 2022 年 5 月 11 日

r needs to be pre-multiplied by P1, not post-multiplied.
P1 = [1,0,0];
eular = [0,pi/2,pi/2];
r = eul2rotm(eular,'ZYX');
destinationPt = P1*r
destinationPt = 1×3
0.0000 1.0000 0.0000
##### 11 件のコメント表示非表示 10 件の古いコメント
Matt J 2022 年 5 月 11 日
Great!

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R2022a

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