Small collection of utility functions for calculating screen size of objects, size of camera frustum at a distance, etc.

CameraMath.cs

using System;
using System.Runtime.InteropServices;
using System.Runtime.CompilerServices;

using Unity.Burst;
using Unity.Mathematics;

public static class CameraMath
{
	/// <summary>
	/// Get the screen size of an object in pixels, given its distance and diameter.
	/// </summary>
	/// <param name="distance">The distance from the desired camera to the object</param>
	/// <param name="diameter">The diameter of the object's bounding sphere</param>
	/// <param name="screenHeight">The height of the screen, in pixels</param>
	/// <param name="fieldOfView">The Field of View (in degrees) of the desired camera</param>
	[MethodImpl( MethodImplOptions.AggressiveInlining )]
	public static float DistanceAndDiameterToPixelSize( float distance, float diameter, float screenHeight, float fieldOfView )
	{
		return math.degrees( diameter * screenHeight ) / ( distance * fieldOfView );
	}

	/// <summary>
	/// Get the distance of an object, given its screen size in pixels and diameter.
	/// </summary>
	/// <param name="pixelSize">The size (in screen pixels) of the object</param>
	/// <param name="diameter">The actual diameter of the object's bounding sphere</param>
	/// <param name="screenHeight">The height of the screen, in pixels</param>
	/// <param name="fieldOfView">The Field of View (in degrees) of the desired camera</param>
	[MethodImpl( MethodImplOptions.AggressiveInlining )]
	public static float PixelSizeAndDiameterToDistance( float pixelSize, float diameter, float screenHeight, float fieldOfView )
	{
		return math.degrees( diameter * screenHeight ) / ( pixelSize * fieldOfView );
	}

	/// <summary>
	/// Returns the calculated diameter of an object, given its screen size in pixels and distance.
	/// </summary>
	/// <param name="pixelSize">The size (in screen pixels) of the object</param>
	/// <param name="distance">The distance from the desired camera to the object</param>
	/// <param name="screenHeight">The height of the screen, in pixels</param>
	/// <param name="fieldOfView">The Field of View (in degrees) of the desired camera</param>
	[MethodImpl( MethodImplOptions.AggressiveInlining )]
	public static float PixelSizeAndDistanceToDiameter( float pixelSize, float distance, float screenHeight, float fieldOfView )
	{
		float diameter = ( pixelSize * distance * fieldOfView ) / math.degrees( screenHeight );
		return diameter;
	}

	/// <summary>
	/// Returns the distance required to give a specified frustum height at the given Field of View.
	/// </summary>
	/// <param name="frustumHeight">The diameter of the object's bounding sphere</param>
	/// <param name="fieldOfView">The Field of View (in degrees) of the desired camera</param>
	[MethodImpl( MethodImplOptions.AggressiveInlining )]
	public static float DistanceForFrustumHeight( float frustumHeight, float fieldOfView )
	{
		float cameraView = math.tan( math.radians( fieldOfView * 0.5f ) );
		float distance = ( frustumHeight * 0.5f ) / cameraView;

		return distance;
	}

	/// <summary>
	/// Returns the height of the frustum at a given distance.
	/// </summary>
	[MethodImpl( MethodImplOptions.AggressiveInlining )]
	public static float FrustumHeightAtDistance( float distance, float fieldOfView )
	{
		return 2.0f * distance * math.tan( math.radians( fieldOfView * 0.5f ) );
	}

	/// <summary>
	/// Returns the field of view when the distance and height are known.
	/// </summary>
	/// <param name="distance">Distance from camera to target position</param>
	/// <param name="height">Height of target</param>
	/// <returns></returns>
	[MethodImpl( MethodImplOptions.AggressiveInlining )]
	public static float FieldOfViewFromDistanceAndHeight( float distance, float height )
	{
		return 2.0f * math.degrees( math.atan( height * 0.5f / distance ) ); 
	}
}