How to Read Elevation from Heightmap

Hi Guys anyone can help me to use correctly "GetPixel" and "ReadPixel" to real the real elevation from heightmap when clicking on mouse plz. i tryed this code : using System.Collections; using System.Collections.Generic; using UnityEngine;

 public class GetValue : MonoBehaviour {
     public Vector3 size = new Vector3(100, 10, 100);
 
     // Use this for initialization
     void Start () {
        
     }
     
     // Update is called once per frame
     void Update () {
         RaycastHit hit = new RaycastHit();
         Ray ray = new Ray();
         ray = Camera.main.ScreenPointToRay(Input.mousePosition);
 
         if (Input.GetMouseButtonDown(0))
         {
            // Debug.Log("mouse down");
             if (Physics.Raycast(ray, out hit))
             {
                 Vector3 hitPos = Camera.main.WorldToScreenPoint(hit.point);
                 //Debug.Log(hitPos + " - " + hit.collider.name);
                 MeshRenderer rend = hit.collider.GetComponent<MeshRenderer>();
                 //Texture to Texture2D
                 Texture mainTexture = rend.material.mainTexture;
                 Texture2D texture2D = new Texture2D(mainTexture.width, mainTexture.height, TextureFormat.RGBA32, false);
 
                 RenderTexture currentRT = RenderTexture.active;
 
                 RenderTexture renderTexture = new RenderTexture(mainTexture.width, mainTexture.height, 32);
                 Graphics.Blit(mainTexture, renderTexture);
 
                 RenderTexture.active = renderTexture;
                 texture2D.ReadPixels(new Rect(0, 0, renderTexture.width, renderTexture.height), 0, 0);
                 texture2D.Apply();
 
                 Color[] pixels = texture2D.GetPixels();
               
                 RenderTexture.active = currentRT;
                 /////
 
 
                 Vector2 pixelUV = hit.textureCoord;
                 float uvX = pixelUV.x * texture2D.width;
                 float uvY = pixelUV.y * texture2D.height;
                 
 
                 Color hitColor = texture2D.GetPixel((int)uvX,(int) uvY);
                 Debug.Log(hitColor + "    " + uvX + "    " + uvY);
                 Vector3 pos = hitPos;
                 int x = Mathf.FloorToInt(hitPos.x / size.x * texture2D.width);
                 int z = Mathf.FloorToInt(hitPos.z / size.z * texture2D.height);
                 pos.y = texture2D.GetPixel(x, z).grayscale;
               
             }
         }
     }
 
 }

result:

RGBA(0.161, 0.161, 0.161, 1.000) 777.5255 438.3657