Direction between 2 Vectors

[Colin]

OK so i have 2 3d vector's

the first is the camera and the second is an object i want to look at, my camera system using the mouse relative position so rot.x = rad offset from 0.

So i've been trying to come up with a function to calculate the Radians from vec1 to vec2 and I just can't seem to get anything to work, can anyone save me from this task as my head is about to explode.

I have the xz rotation working fine using: rV.x := ArcTan2( targ.z - posZ, targ.x - posX ); - altho sometimes it does a full rotation reversal

but i need the y axis also to be correct, looking up or down at the object once it is facing it

[User137]

I had this function in my old codes:

function Angle3D(x1,y1,z1,x2,y2,z2: double): double;
var a: double;
begin
  a:=(x1*x2+y1*y2+z1*z2) /
     ( sqrt(x1*x1+y1*y1+z1*z1) * sqrt(x2*x2+y2*y2+z2*z2) );
  //if a>1 then a:=1 else if a<-1 then a:=-1;
  result:=abs(arccos(a));
end;

It looks slightly unfinished, and i was surprised i didn't clean that up for nxPascal yet. Atleast what i understand, result should always be >= 0. Sqrt insides seem fine, they are always on positive side or 0 so don't need any temp variables either. Not sure what i was thinking with the if-clause.

[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.