Obviously large metal objects like cranes etc are ferrous and therefore have the potential at very close proximity to disturb the magnetic flux acting on the Inspires magnetometer (compass). This can throw up an error which if you are not prepared for can cause issues.
Be prepared for the aircraft to drop into P-Atti mode if the Inspire senses sufficient disturbance in the magnetic field to cause an error.
Alternatively, fly the entire flight in P-Atti and the handling of the aircraft will remain constant.
...Fly2View, I recently flew directly over a Marine Dry-Storage Bldg (Erect Steel type bldg), 325' x 80', crest of the roof was approx 42', i flew btwn (approx) 10'-20' above the roof, with ZERO adverse effects of ctrl or the flight itself...
I fly as close as 10 feet to wind turbines all the time. We inspect them. The worst problem I have is wind gusts that swirl around the top of the nacelle. This one is 300 feet tall and I'm about 15 feet away: