Direction between 2 Vectors

[LP]

I had this function in my old codes:...

Your code is perfectly fine. You don't need ABS in the last line though as ArcCos returns values from 0 to Pi. Values inside SQRT will never be negative as they are elevated to square. Detailed math is explained here. As you can see, your code does exactly that - the first part of code calculates dot product and second part divides it by multiplication of two vector lengths. P.S. if a>1 check was probably due to vectors not being of unitary length, which you should normalize instead.

[Dan]

I dont think the man is looking for an angle between two vectors. He is asking for the following: given two positions (origin and target) in 3d space he needs the Yaw and Pitch values which will orient the camera looking from the origin at the target. Colin, what I think you are looking for is simply: rV.y := ArcSin(Dir.y); where Dir is a normalized direction vector (Dir := normlize(targ.x - posX, targ.y - posY, targ.z - posZ))

[Colin]

Dan, exactly the answer I needed, this is not the first time your post/replies have saved me from myself, I can't thank you enough but thank you very much

@User137, Thanks for your reply, your function will also be useful for other purposes. Thanks.

So my code so far (which works)

//
// sets the look at target of the camera
//
procedure TCameraController.setTarget(const targ: TD3DXMatrix);
var
  pos, rV: TD3DXVector3;
  diff: TD3DXVector3;
begin
  pos := D3DXVector3(targ._41, targ._42, targ._43);

  D3DXVec3Subtract(diff, pos, position);
  D3DXVec3Normalize(diff, diff);

  rV := D3DXVector3(
            arctan2(diff.z, diff.x),
            arcsin(diff.y),
            diff.z
          );

  D3DXVec3Lerp(rotation, rV, rotation, 0.1);
end;

my only problem now is using the DX function MatrixLookAt for matView seems to have a rotation limit on the yaxis.

[LP]

my only problem now is using the DX function MatrixLookAt for matView seems to have a rotation limit on the yaxis.

It could be due to gimbal lock.

[Colin]

I was reading about this a few hours ago and I think you may be right, so I think I will add in some quaternion routines and see if I can solve it. Thanks

[User137]

Glad you got it solved, although not by my tip This is how the function ended up to:

function Angle(v1, v2: TVector): single;
begin
  norm(v1.x, v1.y, v1.z);
  norm(v2.x, v2.y, v2.z);
  result:=arccos(dot(v1, v2));
end;

Didn't test yet, but i realized that normalized vectors, when their length is multiplied is 1. That leaves it with just dot product.

[LP]

Didn't test yet, but i realized that normalized vectors, when their length is multiplied is 1. That leaves it with just dot product.

Actually, dot product of two 3D vectors is an indirect measure of angle between them. So if you need to test some specific cases, you may omit the arccos altogether.