How to get the nearest point on a depth map?

I achieved streaming depth map using ARKit by taking reference to this GitHub code: https://github.com/TokyoYoshida/ExampleOfiOSLiDAR/blob/main/ExampleOfiOSLiDAR/Samples/Depth/DepthMapViewController.swift

Now I would like to find the point which is closest to the rear camera and show the point on the depth map. It is like the codes can automatically detect the closest point and label it when the app is running. How can I get the closest pixel point with ARKit and CVPixelBuffer?