What’s the function of aus in this sentence?
It’s a bit useless to use aus in this sentence, it would work out quite well without it.
I am not quite sure how the purpose the aus serves here is called in grammar terms, I’d assume it is an adverb just as von hier are. My ‘native intention’ tells me that von hier aus is a bit more precise than just von hier and it also implies a contrast (for example compared to a different observation tower in our case) more vividly than von hier would do alone. But the difference is so minor, I don’t even know if there’s a rule describing this.