1. A method of forming a welded structure comprising: arranging on constituent pieces of the structure to be welded on a support surface in a desired configuration, recording at least one image of the arrangement of the constituent pieces on the support surface, determining from the image(s) the positions of a plurality of weld points, welding with welding apparatus the constituent pieces together at said weld points to form the welded structure, and controlling the welding of the constituent pieces with said welding apparatus on the basis of the determined positions of the weld points.