HIGH-EFFICIENCY BUILDING SURVEYS BY DYNAMIC AND STATIC DIGITAL IMAGES ORIENTED WITH “MIXED MODELS” Domenico Visintini Department of Geo-Resources & Territory, University of Udine, via Cotonificio, 114 I-33100 Udine, Italy visintini@dgt.uniud.it KEY WORDS: Architecture, Digital, Surveying, Integration, Rectification, Algorithms, Dynamic ABSTRACT: Throughout this paper, a method to efficiently survey buildings by digital images, dynamically and statically acquired, is presented by investigating methodological and analytical aspects and by suggesting an integrated surveying procedure, in order to well exploit the synergy among different imaging sensors. At first, it is earlier evaluated and then discarded (for described operative reasons) the idea to use exclusively digital images of a Mobile Mapping System to photogrammetrically survey buildings, exploiting them instead to survey 3D-control points only. In this way, classical topographic measures on the facades are no more required. The original “pseudo-dynamic” model allowing this photogrammetric technique of control point positioning, also with a simplified low cost system, is briefly shown. Afterwards, the digital rectification of static CCD images is investigated, taking into account the effect of coordinate errors in control points measured by MMS. This problem can be suitably overcome thanks to an original mixed model algorithm considering also the prediction of control point coordinate simultaneously to parameter estimation of homographic image transformations. At the end, the testing of this integrated survey method to some historical buildings is presented, as well as the operative problems and limitations occurred. In any case and considering image scales involved, the CCD images so rectified on façades planes have a decimeter accuracy, more than satisfactory for a lot of applications as surveys of aggregate buildings or urban blocks. 1. INTRODUCTION This paper presents a method to efficiently survey buildings by means of the integration of digital images acquired either in dynamic or in static way. The central concept is to well 3D or 2D-orient images on control point coordinates photogrammetrically too obtained before thanks to the application of “mixed (estimation and prediction) analytical models” (Dermanis, 1990). Consequently, two main acquisition phases characterize this surveying method: in the first, a low-cost Mobile Mapping System (MMS) is employed to acquire dynamic images of the buildings: these images permit an efficient photogrammetric survey of 3D-points, later usable as control points. Afterwards, by using a higher resolution CCD camera, (classical) static shots are instead achieved; in these other images, same buildings (but in better geometric/resolution conditions) and just before measured control points are portrayed so allowing digital rectification. The analytical and operative steps making possible this integrated survey and the obtainable results will be explained in next chapters. In any case, the field of application has been thought for decimetre accuracy surveys of aggregate edifice and not for more precise/detailed architectonic goals: the realization of façade raster textures of building volume for profitable VRML purposes is a emblematic example in such a sense. This integrated survey has been in reality tested for digital 2D- façades rectification of some historical buildings in Serravalle - Vittorio Veneto (Italy). All paper figures are relating to this case, also those in the analytical chapters, so that to better clarify general methodological topics. 2. MMS TECHNOLOGY AND BUILDING SURVEY In these lasts years, the photogrammetric survey technology by means of MMS, that is terrestrial vehicles equipped with GPS, INS, CCD on other integrated sensors, has had an increasing development and interesting applications, mainly to 3D-survey geometry and pavement characteristics of roadways. This advanced technique, involving completely different measuring sensors (satellite, inertial, odometer, imaging, etc), is obviously characterized by lots of analytical, methodological, and technological sub-aspects. Obviously, this paper can only briefly hint to some of them, forwarding the interested reader to references for deeper investigations: a good starting point of the enormous available literature is surely given from the proceedings of the International Workshops held on this technology (Ohio State University, 1995; Li and Murai, 1999; El-Sheimy, 2001). Anyway, the fundamental innovation introduced by (terrestrial) MMS is the direct orientation of the imaging sensors thanks to its navigation sensors, likewise for analogous aerial systems before improved. In this way, to survey whatever kind of object, a “one time only” moving acquisition of data is sufficient, by simply passing through the interest area with a vehicle. Furthermore, bearing in mind the elevated level of technological instrumentations and analytical models involved in acquiring and processing MMS data, a high efficiency 3D-survey in terms of correctness, accuracy, reliability, completeness, and productivity can be realistically expected. Throughout this chapter is evaluated the idea to use digital images of a MMS to photogrammetrically survey buildings façades and any other interested architectonic entity. Although it looks extremely promising, since removing some measure steps it appropriately increases the automation level of the surveying, on the other hand it unavoidably spawns new operative problems. The new-fangled incoming restrictions, as difficulty to cover a complete surrounding path, buildings too near/distant from a road, fixed shot geometry respect building and/or among successive images, are easily understandable. Nevertheless to make better clear them, supposing to have to survey a certain edifice, following figures report digital images potentially 335 The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol. XXXIV, Part 5/W12