It is a magical feeling to mark the tree and the phone calculates the diameter automatically.
In the app Arboreal Forest you could measure the trees with the new Lidar sensor that is available in the iPhone 12 Pro and Pro Max. The Lidar sensors measure the distance to 600 points. We are detecting the edges of the tree and calculates the diameter.
The app Arboreal Forest measures diameters, basal area, trees per hectare, height, and volumes. A real digital tool that fits in your pocket. It also works on phones without Lidar, but then it uses the camera.
Download it in the App Store and test it yourself.