This afternoon, I thought I could get some really cool footage of my local canal and chose a flat spot near a canal lock to take off. After the usual preflight checks, I turned on the phantom only to be bombarded with a compass error warning and a suggestion to move elsewhere. Unbeknownst to me I moved to a nearly canal bridge but still got the same compass error readout. On further inspection of the lock and the bridge I found their was massive reinforced iron in both structures so I decided to abort the mission. I contemplated whether it would be possible to take of in ATTI mode, if that were possible, but was reluctant to do so due to the enclosed nature of the canal bordered by high trees. I foresaw losing LOS and saying goodbye to my bird. Now my question which I would like to ask the more experienced on the forum. Could I have started in ATTI mode and flown the mission safely by bypassing the start up procedure that gave me all the compass errors in PGP? Many thanks for informed revise in advance.