I used the depth map to pick up the coordinates, but it didn't work

In this example, the scene. pick method is used to pick up the scene coordinates when the mouse is moving. Considering the performance of scene. pick, I used depth maps to calculate the scene coordinates. I have seen this GPU picking point and normal example And I only need to obtain the position, no normals. So I calculated coordinates from the depth map based on the code in the example, but it was not successful.