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c++math3dtrigonometryangle

C++ Calculate Angle (0 to 360) Between Two 3D Vectors

Let's say I have 2 3D Vectors

Vec3 v1, v2;

v1.x = 203;
v1.y = 355;
v1.z = 922;

v2.x = 6;
v2.y = 13;
v2.z = 198;

How would I calculate the angle between v1 & v2? I.e. the final answer would be within 0 to 360

I've tried

Vec3 angle = v1 - v2;

And a few other things but I just can't seem to get it working correctly.

Solution

  • You need to use the dot product for this, and once you have that you can follow the standard method. Example:

    #include <cmath>

float dot(Vec3 a, Vec3 b)  //calculates dot product of a and b
{
    return a.x * b.x + a.y * b.y + a.z * b.z;
}

float mag(Vec3 a)  //calculates magnitude of a
{
    return std::sqrt(a.x * a.x + a.y * a.y + a.z * a.z);
}

int main()
{
    Vec3 v1, v2;

    v1.x = 203;
    v1.y = 355;
    v1.z = 922;

    v2.x = 6;
    v2.y = 13;
    v2.z = 198;

    float angle = std::acos(dot(v1,v2)/(mag(v1)*mag(v2)));
}