Rather math question...

[nerexis]

I need to obtain angle between 2 vectors (waypoints...) but i dont know if im doing that corectly because it returns strange angle like 0,00015 or something like that.

So is it correct way of calculating angle?

Example waypoints:
1. 373.735474 -5148.517578 -1.944246
2. 366.841614 -5157.729980 3.432772

Function:

    float AngleTo(const Vector3df& q)
    {
        Vector3df v1(this->X,this->Y,this->Z);
        Vector3df v2(q);

        float v1_magnitude = sqrt(v1.X*v1.X + v1.Y*v1.Y + v1.Z*v1.Z);
        float v2_magnitude = sqrt(v2.X*v2.X + v2.Y*v2.Y + v2.Z*v2.Z);

        float d = v1.DotProduct(v2);

        float t = acos(d/v1_magnitude*v2_magnitude); 

        return t*PI/180;
    }

[lanman92]

Uhhh, Math.Atan2(float a, float b)? It's a lot easier than doing it THAT way.

EDIT:
You're using C++, so just include math and use atan2(...).

[namreeb]

Just to add to lanman92's response, you want to do atan2(y2-y1, x2-x1) ... or maybe its the reverse of that: atan2(x2 - x1, y2 - y1).

[nerexis]

Huh, isnt it for facing angle? I want angle on Z axis, I mean to detect if way between two vectors is walkable so angle between them should be < 50 degress.

Look at screenshot:

[Azzie2k8]

I know the code I am about to post is just ugly and there are faster ways to do this but maybe this explains the math a bit better

	float disty = Target->Position.fX - MyPosition.fX;
	float distx = Target->Position.fY - MyPosition.fY;

	if (distx > 0 && disty > 0)
	{
		face = abs(atan( distx / disty ));
	}
	else if (distx > 0 && disty < 0)
	{
		face = (0.5 * 3.14) + abs(atan( disty / distx ));
	}
	else if (distx < 0 && disty < 0)
	{
		face = (1 * 3.14) + abs(atan( distx / disty ));
	}
	else if (distx < 0 && disty > 0)
	{
		face = (1.5 * 3.14) + abs(atan( disty / distx ));
	}

btw thats obviously in radians so you will need to convert it to degrees if you want to

edit: note that the change of X and Y coordinates is wanted since my layout was different than wows layout.

face is the direction your charecter needs to face if he wants to lookt at the object/point

not sure if this answers your question but if you go ahead and change it to fit your approach it will do the job

but you should consider using atan2 like they said

In trigonometry, the two-argument function atan2 is a variation of the arctangent function. For any real arguments x and y not both equal to zero, atan2(y, x) is the angle in radians between the positive x-axis of a plane and the point given by the coordinates (x, y) on it. The angle is positive for counter-clockwise angles (upper half-plane, y > 0), and negative for clockwise angles (lower half-plane, y < 0).

http://en.wikipedia.org/wiki/Atan2

[lanman92]

Just use atan2(z2 - z1, 0). I think that should work?

[nerexis]

Why? Isn't angle dependent on X,Y too?

[Azzie2k8]

Why? Isn't angle dependent on X,Y too?

mh if you you rotate the unit circle it will actually match z coordinates...I think it will also work with atan2 you will only need to figure out what is what

I think it will work

Just try atan2(10,0) giving you about 0,5*pi meaning you will need to face straight up. so you could simply make it work with atan2(DstanceToYourToonOnZ,DistanceToYourToonOnX)

edit: i didnt give it much thought so I might be wrong in the parameters but I am positive that it will work with atan2

[lanman92]

Okay, gotta stop posting so early.... It's acos(sqrt((v2.x * v1.x)^2 + (v2.y * v1.y)) / |v2 - v1|). |v| is magnitude of vector v. That's right, I believe.

[nerexis]

Looks like its wrong.

I made function based on your suggestion, tried to calculate angle between vectors i posted in 1 first post and it doesn't work.

Returns -1.#IND00 :P

Function:

    float AngleTo(const Vector3df& q)
    {
        Vector3df v1(this->X,this->Y,this->Z);
        Vector3df v2(q);

        return acos(sqrt( (v2.X * v1.X) + (v2.Y * v1.Y)) / v2.Magnitude() - v1.Magnitude() )*180/PI;
    }

Why '^2'?..

[lanman92]

Wow. I'm having a bad math day... It's v2.x - v1.x and v2.y - v1.y. You square those results and add them, then sqrt that. It's just the distance formula.

[Azzie2k8]

Looks like its wrong.

I made function based on your suggestion, tried to calculate angle between vectors i posted in 1 first post and it doesn't work.

Returns -1.#IND00 :P

Function:

    float AngleTo(const Vector3df& q)
    {
        Vector3df v1(this->X,this->Y,this->Z);
        Vector3df v2(q);

        return acos(sqrt( (v2.X * v1.X) + (v2.Y * v1.Y)) / v2.Magnitude() - v1.Magnitude() )*180/PI;
    }

Why '^2'?..

I think your first appraoch is right.

The angle between 2 vectors is defined by

cos(a) = abs(vec1 * vec2) / ( abs(vec1) * abs(vec2) )

which means

cos(a) = abs(vec1.x * vec2.x + vec1.y * vec2.y + vec1.z * vec2.z + ) / ( sqrt(vec1.x^2 + vec1.y^2 + vec1.z^2) * sqrt(vec2.x^2 + vec2.y^2 + vec2.z^2) )

edit

This is what a code could look like

acos( abs(vec1.x * vec2.x + vec1.y * vec2.y + vec1.z * vec2.z + ) / ( sqrt( pow(vec1.x,2) + pow(vec1.y,2) + pow(vec1.z,2) ) * sqrt( pow(vec2.x,2) + pow(vec2.y,2) + pow(vec2.z,2) ) ) )

[!@^^@!]

here's one way that works to calc the angle between 2 3D points/ 3D vectors depending on how you look at the problem:

[nerexis]

Omfg O_O WORKS!

Your's formula pwned world and made one of bots better!

Thank you x1000

[alynel]

The maths in your first post was right, you've gotta put brackets around (v1_magnitude*v2_magnitude) though