Unity's radar effect: renders object which are just detected and then disable the renderer (out of the radar field of view).

radarEffect.cs

// Author: Fabien ROUALDES
// Date: 31/01/2016
//
//
// Render objects which are in the radar field of view.
// The radar is rotating around a camera
//

using UnityEngine;
using System.Collections;

public class Radar : MonoBehaviour {
    private Collider[] m_enteringRadar;
    private Collider[] m_leavingRadar;

    public LayerMask m_radarLayerMask;

    public Camera m_radarCamera;
    public Light m_lightEffect;

    private Transform m_cameraTransform;
    private Transform m_lightTransform;

    private float m_angleOffSet;
    private float m_halfExtents;
    private Vector3 m_halfExtentsBox;
    private float m_step;
    private float m_delay;
    private float m_delayDegree;

    // private int cameraDepth;
    // private int cameraHeight;

    // Use this for initialization
    void Start () {
        m_cameraTransform = m_radarCamera.GetComponent<Transform>();
        m_lightTransform = m_lightEffect.GetComponent<Transform>();

        m_angleOffSet = 45f;

        m_halfExtents = 100f;
        m_halfExtentsBox = new Vector3(0.01f, m_halfExtents, m_halfExtents);

        m_step = Mathf.PI / 64f;
        m_delay = Mathf.PI;
        m_delayDegree = m_delay * 180f / Mathf.PI;
        
    }
	
	// Update is called once per frame
	void Update () {
        float inAngle = m_angleOffSet;
        float outAngle = m_angleOffSet - m_delay;

        float inAngleDegree = inAngle * 180.0f / Mathf.PI;
        float outAngleDegree = inAngleDegree - m_delayDegree;

        Vector3 positionIn = new Vector3(m_cameraTransform.position.x + Mathf.Sin(inAngle) * m_halfExtents, 0f, m_cameraTransform.position.z + Mathf.Cos(inAngle)* m_halfExtents);
        Vector3 positionOut = new Vector3(m_cameraTransform.position.x + Mathf.Sin(outAngle) * m_halfExtents, 0f, m_cameraTransform.position.z + Mathf.Cos(outAngle) * m_halfExtents);


        //
        // Radar effects    
        //

        // Rotate "radar emission source"
        m_lightTransform.rotation = Quaternion.Euler(0f, inAngleDegree, 0f);

        // Display detected objects
        m_enteringRadar = Physics.OverlapBox(positionIn, m_halfExtentsBox, Quaternion.Euler(0f, inAngleDegree, 0f), m_radarLayerMask, QueryTriggerInteraction.UseGlobal);
        foreach (Collider c in m_enteringRadar)
        {
            c.gameObject.GetComponent<MeshRenderer>().enabled = true;
        }

        // Loss detected objetcs
        m_leavingRadar = Physics.OverlapBox(positionOut, m_halfExtentsBox, Quaternion.Euler(0f, outAngleDegree, 0f), m_radarLayerMask, QueryTriggerInteraction.UseGlobal);
        foreach (Collider c in m_leavingRadar)
        {
            c.gameObject.GetComponent<MeshRenderer>().enabled = false;
        }

        m_angleOffSet += m_step;
    }
}