Transforms position from world space into viewport space.

Viewport space is normalized and relative to the camera. The bottom-left of the camera is (0,0); the top-right is (1,1). The z position is in world units from the camera.

	// Finds out whether target is on the left or right side of the screen
	var target : Transform;
	
	function Update () {
		var viewPos : Vector3 = camera.WorldToViewportPoint (target.position);
		// viewport coordinates range from zero to one
		if( viewPos.x > 0.5 )
			print ("target is on the right side!");
		else
			print ("target is on the left side!");
	}

using UnityEngine;
using System.Collections;

public class Example : MonoBehaviour {
    public Transform target;
    void Update() {
        Vector3 viewPos = camera.WorldToViewportPoint(target.position);
        if (viewPos.x > 0.5F)
            print("target is on the right side!");
        else
            print("target is on the left side!");
    }
}

import UnityEngine
import System.Collections

public class Example(MonoBehaviour):

	public target as Transform

	def Update() as void:
		viewPos as Vector3 = camera.WorldToViewportPoint(target.position)
		if viewPos.x > 0.5F:
			print('target is on the right side!')
		else:
			print('target is on the left side!')