Digital wide scale orthoprojections and mapping from low-height aerial images

Orthoprojection and automatic or semiautomatic DEM productions are digital photogrammetrical products that enable two ranges of requirements in close-range survey applied to architecture and archaeology, to be connected. It is possible to depict both the shape of objects and the thematic data derived from orthoprojection; photographic information in fact enhances documentation as it other details on the masonry typology, the kind of facing the decorations, the materials and their decay. The non-conventional methodology analyzed in this paper, and the consequent orthophotos and stereo-plotting production, are based on the use of a restrained helium balloon, which was equipped with an ad hoc remote-controlled platform. A non-metrical film-based camera was placed inside the platform to acquire nadiral images of overflow areas. The still problematic phases of the application of these methodology will be discussed: the plan of the stereoscopic stripes which is rendered complicated by system instability, the non-metric camera calibration, the surface model generation and their solution according to the morphology of the surveyed area. Finally, the accuracy evaluation of the final orthoimaging will be dealt together with the opportune integration of this kind of work in a multiscale spatial information system.