Check if the camera is focused on a sprite - unity3d

Question

I am writing a Cardboard game in Unity and I want to check whether my camera is facing a sprite or not. I have written the following code:
private void GetSphericalCoordinates(Vector3 vector, out float tetta, out float fi)
{
float r = Mathf.Sqrt(vector.x * vector.x + vector.y * vector.y + vector.z * vector.z);
tetta = Mathf.Acos(vector.z / r);
fi = Mathf.Atan2(vector.y, vector.x);
}
public bool IsLookingAtMe(Vector3 point, Quaternion angle)
{
Vector3 topLeftPoint = new Vector3(transform.position.x - transform.localScale.x / 2, transform.position.y - transform.localScale.y / 2);
Vector3 topRightPoint = new Vector3(transform.position.x + transform.localScale.x / 2, transform.position.y - transform.localScale.y / 2);
Vector3 bottomLeftPoint = new Vector3(transform.position.x - transform.localScale.x / 2, transform.position.y + transform.localScale.y / 2);
Vector3 bottomRightPoint = new Vector3(transform.position.x + transform.localScale.x / 2, transform.position.y + transform.localScale.y / 2);
float topLeftTetta, topRightTetta, bottomLeftTetta, bottomRightTetta, lookTetta;
float topLeftFi, topRightFi, bottomLeftFi, bottomRightFi, lookFi;
GetSphericalCoordinates(topLeftPoint - point, out topLeftTetta, out topLeftFi);
GetSphericalCoordinates(topRightPoint - point, out topRightTetta, out topRightFi);
GetSphericalCoordinates(bottomLeftPoint - point, out bottomLeftTetta, out bottomLeftFi);
GetSphericalCoordinates(bottomRightPoint - point, out bottomRightTetta, out bottomRightFi);
lookTetta = angle.eulerAngles.x * Mathf.Deg2Rad;
lookFi = angle.eulerAngles.y * Mathf.Deg2Rad;
if (lookTetta >= topLeftTetta && lookTetta <= bottomRightTetta)
return true;
return false;
}
In my code I find the 4 angles of my sprite, which is a square, so I have 5 points which make a pyramid. Now I need to check whether my camera is inside my pyramid or not.
The problem is, my lookTetta and lookFi never goes inside my pyramid. I just checked the Tetta only.
Please help me with it.

Answer 1

Using WorldToViewportPoint it should be a single statement. No need to deal with viewing cones manually.
Project the sprite world position to viewport position, then lookup if it is within bounds (ignoring z).
public bool IsMainCameraLookingAtMe()
{
Bounds viewportBounds = new Bounds.SetMinMax(Vector2.zero, Vector2.one);
return viewportBounds.Contains((Vector2)Camera.main.WorldToViewportPoint(transform.position));
}
May check each sprite corner individually to fit your needs.

Answer 2

I have used IntersectRay using the code below:
public bool IsLookingAtMe(Vector3 origin, Vector3 direction)
{
Bounds bounds = GetComponent<Renderer>().bounds;
Ray ray = new Ray(origin, direction);
return bounds.IntersectRay(ray);
}