How to get the direction of a projected velocity?

[Nanako]

I have a desired direction A, and i have a body which is moving at a certain velocity B which might be moving in that direction, or might be moving away.

I need to know how much velocity towards the target, the body has. This seems simple enough to begin with;

Vector3 C = Vector3.Project(B,A);

That gives me a vector, great.
But if i check C.Magnitude, it’s always going to be a positive value. the magnitude tells me how fast towards OR away from the target direction my object is going. But that’s not helpful. I need to know only how far towards. If magnitude could be negative, with a negative value indicating it’s moving away, then that would be helpful. But it cannot.

What can i do in this situation to get the information i need?

[LeftyRighty]

Unity - Scripting API: Vector3.Dot

tells you towards / away as a +1/-1, multiple the magnitude by that.

[Nanako]

that was very helpful, thank you

Roughly it works like this now:

Vector3 C = Vector3.Project(B,A);
float D = C.magnitude * Vector3.Dot(A.normalized, B.normalized);

[Necronomicron]

@Nanako

that was very helpful, thank you

Roughly it works like this now:

Vector3 C = Vector3.Project(B,A);
float D = C.magnitude * Vector3.Dot(A.normalized, B.normalized);

It seems it should be:

float D = C.magnitude * Mathf.Sign(Vector3.Dot(A.normalized, B.normalized));

[angelonit]

Still useful! Just used this to make a function that clamps the velocity in the relative axes of my character:

public void ClampVelocity(Vector3 v3Min, Vector3 v3Max)
{
Vector3 v3Sign = new Vector3(Mathf.Sign(Vector3.Dot(velocity, charTransform.right)), Mathf.Sign(Vector3.Dot(velocity, charTransform.up)), Mathf.Sign(Vector3.Dot(velocity, charTransform.forward)));

velocity = (charTransform.right * Mathf.Clamp(v3Sign.x * Vector3.Project(velocity, charTransform.right).magnitude, v3Min.x, v3Max.x)) + (charTransform.up * Mathf.Clamp(v3Sign.y * Vector3.Project(velocity, charTransform.up).magnitude, v3Min.y, v3Max.y)) + (charTransform.forward * Mathf.Clamp(v3Sign.z * Vector3.Project(velocity, charTransform.forward).magnitude, v3Min.z, v3Max.z));
}

[Kurt-Dekker]

@angelonit

Vector3 v3Sign = new Vector3(Mathf.Sign(Vector3.Dot(velocity, charTransform.right)), Mathf.Sign(Vector3.Dot(velocity, charTransform.up)), Mathf.Sign(Vector3.Dot(velocity, charTransform.forward)));

velocity = (charTransform.right * v3Sign.x * Mathf.Clamp(Vector3.Project(velocity, charTransform.right).magnitude, v3Min.x, v3Max.x)) + (charTransform.up * v3Sign.y * Mathf.Clamp(Vector3.Project(velocity, charTransform.up).magnitude, v3Min.y, v3Max.y)) + (charTransform.forward * v3Sign.z * Mathf.Clamp(Vector3.Project(velocity, charTransform.forward).magnitude, v3Min.z, v3Max.z));

WOW!

If you have more than one dot (.) on a line, you’re just being mean to yourself.

How to break down hairy lines of code:

http://plbm.com/?p=248

Break it up, practice social distancing in your code, one thing per line please.

[angelonit]

@angelonit

Still useful! Just used this to make a function that clamps the velocity in the relative axes of my character:

public void ClampVelocity(Vector3 v3Min, Vector3 v3Max)
{
Vector3 v3Sign = new Vector3(Mathf.Sign(Vector3.Dot(velocity, charTransform.right)), Mathf.Sign(Vector3.Dot(velocity, charTransform.up)), Mathf.Sign(Vector3.Dot(velocity, charTransform.forward)));

velocity = (charTransform.right * Mathf.Clamp(v3Sign.x * Vector3.Project(velocity, charTransform.right).magnitude, v3Min.x, v3Max.x)) + (charTransform.up * Mathf.Clamp(v3Sign.y * Vector3.Project(velocity, charTransform.up).magnitude, v3Min.y, v3Max.y)) + (charTransform.forward * Mathf.Clamp(v3Sign.z * Vector3.Project(velocity, charTransform.forward).magnitude, v3Min.z, v3Max.z));
}

Modified because the “v3Sign” multiplier has to be inside the clamp