I'm in the US and I know the rule is 400 feet. However, what exactly does that apply to? For instance, I'd like to shoot some bridge shots. I plan to launch from a trail below the bridge. The top of the bridge deck is about 150 feet about where I'm launching from. Can I go 400 feet above the bridge (i.e. 550 feet above my launch point) or can I only go 250 feet above the bridge (400 feet above my launch point)?