Instead, you should just figure out what the degrees of the top of your blocking items are and set that as a limit. If the tops of trees mean something needs to be at least 30° above the horizon, then use that value. If your neighbor's house means it needs to be 60°, then use that value. Being allowed to say 30° to the east, 60° to the west, etc would be even better. Imaging your yard and having to decipher all of that would be way overkill and totally unnecessary.