Praise then darkness, and creation unfinished

Not very much trouble, I think, so long as you make it obvious that you are neither stealing the thing nor damaging it. I would suggest writing a note along the lines of "Please do not block the ramp with your theodolite," and attach it with string or tape. (If the surveyor is across the street, they will come back while you're attaching the the note. But I don't think this is likely.) Then move the instrument a few feet, as needed.