Angle between 2 Vectors

[Schoppy0384]

Hi,

I need the Angle between a Plane and the Camera:

 

Leadwerks::Vec3 V1 = mPlane->GetPosition();
Leadwerks::Vec3 V2 = camera->GetPosition();

// turn vectors into Normals
Leadwerks::Vec3 V1n = V1.Normalize();
Leadwerks::Vec3 V2n = V2.Normalize();

//the Dot Product
float dot = V1n.Dot(V2n);

//And the Angle
float angle = Leadwerks::Math::ACos(dot);

 

But the Angle is not correct.

[Guppy]

Well V1 is not contained in mPlane so what did yiubexpect?

[shadmar]

mPlane and camera vectors are just positions which you have normalized, and it doesn't make any sense.

What are you trying to achieve?

[Vulcan]

Try using Math:Atan2, if I remember correctly you get the angle between them.

[Vulcan]

This might:

float tRoty;

// Calculate angle from point A towards point B
Vec3 tv = secondEntity.GetPosition - entity->GetPosition();
tRoty = Math::ATan2(tv.x, tv.z);

[Josh]

The dot product ranges from -1 to 1, so I think the angle might something like this:

angle = (1.0 + a.Dot(B)) * 90.0

 

That way -1 would give an angle of zero and +1 would give an angle of 180.

 

You might have to flip the sign. +/-

[DerRidda]

Hi,

I need the Angle between a Plane and the Camera:

 

Leadwerks::Vec3 V1 = mPlane->GetPosition();
Leadwerks::Vec3 V2 = camera->GetPosition();

// turn vectors into Normals
Leadwerks::Vec3 V1n = V1.Normalize();
Leadwerks::Vec3 V2n = V2.Normalize();

//the Dot Product
float dot = V1n.Dot(V2n);

//And the Angle
float angle = Leadwerks::Math::ACos(dot);

 

But the Angle is not correct.

 

The angle is correct, you are just feeding it the wrong values for what I assume you want to do.

This is the angle you are actually calculating:

https://docs.google.com/file/d/0B3jPhxJap2Y3QUN2aTBldWZMZGc/

[Schoppy0384]

Ok, i need exactly this effect:

[Guppy]

Point distance to plane:

[DerRidda]

That video explains it quite nicely, as you can see, the plane is the point from which everything is calculated.

 

One correction about the dot product

a*b=abs(a)*abs(b )*cos(phi) thus acos(a*b/(abs(a)*abs(b )))=phi

(Watch for divide by zero situations!)

which is essentailly what you do already but with the wrong values.

 

As the video shows, you need the normal of that plane and the distance plane to camera.

 

That nebula effect is really cool btw.

[Josh]

That's a good technique for volumetric spotlight effects, too. Source engine uses it for headlights and stuff like that.

[AggrorJorn]

As a side note to the OP, a 'normalized' vector is not the same thing as the normal vector.

 

Vec3:Normalize returns a vector which is normalized (brought back to values of 1).

Vec3:Cross returns the cross product aka the normal vector.

[Guppy]

Vec3:Normalize returns a vector which is normalized (brought back to length of 1).

[Schoppy0384]

Ok, thanks all for help.

 

I think I have the solution:

 

//Get the Plane Normal
Surface* surface = mPlane->GetSurface(0);
Leadwerks::Vec3 V1 = surface->GetVertexNormal(1);
//Get the Differenz between Camera and Plane
Leadwerks::Vec3 V2 = camera->GetPosition() - mPlane->GetPosition();

//Normalize the Vectors
V1 = V1.Normalize();
V2 = V2.Normalize();

//The Dot Product
float dot = V1.Dot(V2);

//ABS
float dotAbsolute = Leadwerks::Math::Abs(dot);

cout << dotAbsolute << endl;

mPlane->SetColor(1, 1, 1, dotAbsolute);

[Schoppy0384]

Hi,

another problem. After rotating the Plane, the Effect don't work.

 

Are the VertexNormal are not rotating too?

[Ma-Shell]

I would guess, they are in object space. In that case you would have to multiply them by the transformation matrix of your entity.