# How do you convert World Position to Field of View angle.

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I am doing some camera calculations and would like to convert the target's world position into Offset angles from the center of the screen, based off of the veritcal and horizontal Field Of View.

this picture explains what I am after:

[attachment=17453:FOVAngles.png]

I tried getting spherical coordinates by converting cartesian to spherical, but it isnt exactly right, since i want them to be offsets from the center of the screen and those angles are not. I AM able to convert any viewport point to offset angles, and could convert the target to a viewport point as well, but that would get weird results when the character is not in the field of view.

Maybe i can add an offset to theta of the spherical coord to get its orgin at the center of the screen?

Here is code i have so far which i know is wrong but will provide context with what i am attempting to do.

Vector2 zeroOffset = new Vector2(CameraGame.HorizontalFov / 2, Camera.main.fieldOfView / 2);

Vector3 charPosViewSpace = Camera.main.worldToCameraMatrix * target.position;
charPosViewSpace += Camera.main.transform.position;

//Convert View Space Postion to Spherical Coordinate.
float r =
Mathf.Sqrt((charPosViewSpace.x * charPosViewSpace.x) +
(charPosViewSpace.y * charPosViewSpace.y) +
(charPosViewSpace.z * charPosViewSpace.z));

float S = Mathf.Sqrt((charPosViewSpace.x * charPosViewSpace.x) +
(charPosViewSpace.y * charPosViewSpace.y));

float phi = Mathf.Rad2Deg * Mathf.Acos(charPosViewSpace.z / r);
float theta;
if (charPosViewSpace.x < 0)
{
theta = Mathf.Rad2Deg * (Mathf.PI - Mathf.Asin(charPosViewSpace.y / S));
} else
{
theta = Mathf.Rad2Deg * Mathf.Asin(charPosViewSpace.y / S);
}

Debug.Log("xAngle: " + theta + " yAngle: " + phi);
Debug.Log("SafeZone: " + SafeZone);



Here is how i get viewport coords to FOV angles:

public void calcAngles()
{

Vector2 zeroOffset = new Vector2(CameraGame.HorizontalFov / 2, Camera.main.fieldOfView / 2);

minRange = new Vector2(CameraGame.HorizontalFov * x1 - zeroOffset.x,
CameraGame.HorizontalFov * y1 - zeroOffset.y);
maxRange = new Vector2(CameraGame.HorizontalFov * x2 - zeroOffset.x,
CameraGame.HorizontalFov * y2 - zeroOffset.y);
}

Edited by AverageJoeSSU

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The function you want to use to convert a 2D vector to an angle is atan2. If you have trouble using it, post a particular example of coordinates and I'll show you how to use it to compute the angles. But you can probably figure it out by yourself.

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Hmm, i have never used that before but the concept makes sense....

I have two examples: lets say in view space, Coords (-5,5,10) (z is into the screen)

and then behind the camera 5,0,-10

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To compute the angle along the x axis, use atan2(x,z). In this case, atan2(-5,10) = -0.463648 or, if you prefer, -26.5651 degrees.

Similarly for the angle along the y axis, use atan2(y,z). atan2(5,10) = 0.463648 = 26.5651 degrees.

Does that make sense?

EDIT: Oh, in the case of (5,0,-10) you get angles of 153.435 degrees and 180 degrees. Is that what you expected? Edited by Álvaro

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Yes that is what i would expect... i'm gonna plug this into my code and see what i get. Thanks!

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Awesome, just updated my code and the horizontal offset is working perfectly. I think vertical is working too.

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