How To Get Depth Map as Texture2D?

hi, here I have a problem with get Camera's depth texture, after a hole day google it, nothing I got..
I want to get depth map from a camera and get it to Texture2D,
here is my code;

Code (CSharp):

1.  
2.         public Camera cam;
3.         public RenderTexture targetColorBuffer;
4.         public RenderTexture targetDepthBuffer;
5.         public Texture2D tex2D;
6.  
7.  
8.         [Button(ButtonSizes.Large)] // button shows in inspector
9.         public void DepthMap()
10.         {
11.             cam.depthTextureMode = DepthTextureMode.Depth;
12.             cam.clearFlags = CameraClearFlags.Skybox;
13.  
14.             if(targetColorBuffer == false)
15.             {
16.                 targetColorBuffer = new RenderTexture(1024, 1024, 32, RenderTextureFormat.ARGB32);
17.                 targetColorBuffer.Create();
18.             }
19.             if(targetDepthBuffer == false)
20.             {
21.                 targetDepthBuffer = new RenderTexture(1024, 1024, 32, RenderTextureFormat.Depth);
22.                 targetDepthBuffer.Create();
23.             }
24.  
25.             cam.SetTargetBuffers(targetColorBuffer.colorBuffer, targetDepthBuffer.depthBuffer);
26.             cam.Render();
27.             cam.targetTexture = null;
28.  
29.             if(tex2D == false)
30.             {
31.                 tex2D = new Texture2D(1024, 1024, TextureFormat.RFloat, false);
32.             }
33.  
34.             tex2D.LoadRawTextureData(targetDepthBuffer.depthBuffer.GetNativeRenderBufferPtr(), 1024 * 1024 * 4);
35.             tex2D.Apply();
36.         }

it dose some times crash the editor, some times not. and the [targetColorBuffer] and [targetDepthBuffer] shows correct in inspector, but the tex2D is looks like Gaussian noise map....

any ideas about it? thanks for any reply

 

runs on Unity2017.3 Editor Mode