TRUE ORTHOPHOTO OF THE WHOLE TOWN OF TURIN

Abstract

The wide diffusion of modern GIS/LIS instruments requires new geomatical techniques that allow also to unskilled operators the use of such powerful tools. Digital orthophoto is a cheap and efficient product able to integrate GIS/LIS applications with a rigorous photographic representation of urban areas. In large-scale mapping applications, especially where complex architectural objects have to be represented, the problem becomes complicated because there are many discontinuity lines (break-lines) and hidden areas. This requires a more sophisticated orthoprojection procedure, called “true orthophoto”. In recent years, the authors have developed and presented (CIPA, 2001) an original procedure to produce true orthophotos using a “dense DEM” (DDEM) and all the images available in the photogrammetric block (“multi-image” procedure). A software package able to resolve this purpose has been implemented in Visual Fortran and optimised for practical mapping application. It consists in two modules: − ACCORTHO (=ACCurate ORTHOphoto), to produce rigorous digital orthophotos starting from multiple images and a DDEM; − GENEDDEM (GENEration of a DDEM), able to build a dense DEM (suitable for ACCORTHO) from a 3D digital map, using sophisticated interpolation techniques. This paper describes in detail the structure of the GENEDDEM and a practical application of both the programmes for a relevant mapping project, that is still in progress: a true orthophoto of the whole town of Torino (about 5000 ha), in scale 1:2.000, containing many complex architectural objects (Mole Antonelliana, the Gran Madre Church, the Holy Shroud Cathedral).