Angle between two vectors in 3d (2024)

Thanks simon :)

actually i have seen this thread before and confused with

angle = atan2(norm(cross(a,b)), dot(a,b))

and

acos(dot(v1, v2) / (norm(v1) * norm(v2)))

The ATAN2 approach has a higher numerical stability, but it is slower. Although Matlab states in the documentation, that ACOS from the FDLIBM library is use, I cannot reproduce the results exactly using the source from netlib.org. But the differences concern the angles very near to 0 and 180 degrees.

hey simon I have some questions if i have 3values of x,y,z how can i find angle between two 3d vectors?

I have u1 v1 w1(velocity components) volumetric data. Size of u1 is NxNxN (N is 100) and same is true frol v1 and w1.

I have one more case of u2, v2, w2, each one of size NxNxN. both these data sets are obtained from TriScatteredInterp and meshgrid. Basically i plotted streamlines for these two cases and now i want to see how much deviation is there between these streamlines (from case 1 to 2.). I need to find the angle between them at the points given by meshgrid. But cross product wont work (A and B must have at least one dimension of length 3.).. any suggestion ?? Thanks a lot

@Bineet_Mehra: Please open a new thread for a new problem. Otherwise you cannot accept an answer as a solution.

I guess you want:

Now the cross-product should work.

@Jan Simon, Thanks for your suggestion. I shall open a new thread and will try the solution given by you.

Thanks

@Jan the CSSM thread you linked does not exist anymore.

Do you happen to have an archived link for that thread?

I am unable to find the thread by simply searching the title, on the Google Groups (CSSM archive)

I have 3 points in a line( suppose) and one calculations point separately. A(1,1,1)B(2,2,2)C(3 3 3) in a line and P( 5 5 5) as separate. I want to calculate angle A which is subtended by distance AP. And similar for BP,CP. Is it possible to find angles or make program to calculate these angles at once?

Thanks actually i have seen the post referred by Jan simon

and confused that what is the difference between

angle = atan2(norm(cross(a,b)), dot(a,b))

and

acos(dot(v1, v2) / (norm(v1) * norm(v2)))

Mathematically identical, but numerically more stable, when the vectors have very different lengths:

acos(dot(v1 / norm(v1), v2 / norm(v2)))