Unfortunately the documentation for this is not easily available anywhere, but after contacting Ouster support, they sent us a document that defines the possible channel setups for the OS-16 lidar units and based on that it seems like the indexing can start at index 0, 1, 2, or 3, and there are also different setups available (that you can ask for when buying the lidar) where the 16 channels of your lidar are not spaces uniformly and instead they form a tighter beam around the horizon or below the horizon.
