Calculate 3D angles?

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mlsnyder08
mlsnyder08 2017-3-30
回答： Ryan Plucinski 2019-2-14
I have a 40x12 matrix in MatLab. The first three columns represent the (x,y,z) coordinates of the hip, columns 4-6 represent the (x,y,z) coordinates of the knee, and columns 7-9 represent the (x,y,z) coordinates of the ankle. I want to calculate the angle formed between the hip-knee and knee-angle segment.
I know that I can simply use Pythagorean theorem for x,y,z to get the lengths and then use acos to get the angle, but I'd like to do it in a more advanced way with vectors!!!
1) How can I turn certain rows and columns of data from my big matrix into a vector?
2) How can I use those vectors (hip-knee and knee-ankle) to calculate a 3D angle?
Thank you so much!

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回答（2 个）

KSSV
KSSV 2017-3-30
  1 个评论
mlsnyder08
mlsnyder08 2017-3-31
Thank you for the link. I saw that question before but wanted to know how to selectively choose certain rows and columns from my big matrix with which to populate the vector. At that point, I will be able to use the answer from the link you provided.

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Ryan Plucinski
Ryan Plucinski 2019-2-14
1). you can do this in numerous ways, depending on how you want you vector to be.
ex: this code takes the first 3 hip coordinates and seperates them to a different vector, HipX, HipY, and HipZ respectively
%data=excel file of 40x12
data=xlsread('excelfile.xls');
HipX=excelfile(:,1);
HipY=excelfile(:,2);
HipZ=excelfile(:,3);

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