Tan of Field of view

Question

I would like to know what does the tan angle of field of view does. I have seen the following line of code which I'm trying to better understand,

float fovLeft = Mathf.Tan(-outerFieldOfView * Math.PI / 180);
float fovTop = Mathf.Tan(-upperFieldOfView * Math.PI / 180);
float fovRight = Mathf.Tan(-innerFieldOfView * Math.PI / 180);
float fovBottom = Mathf.Tan(-lowerFieldOfView * Math.PI / 180);

whereas outerFieldOfView is in degrees towards the side of the screen. I suppose that it is used to find the angle of view. is my understanding right? what exactly the tan of the field of view refer to?

Answer 1

Following what parameters you know, the tangent could give the angle or deep or size of FOV:

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