Chapter 26 Building surveying for as-built modeling J¨ org Blankenbach * Abstract Building surveying is an important element for as-built documentation as well as for planning and construction in existing contexts. In connection with BIM, however, building surveying faces new challenges. In the past, the results of survey- ing were typically two-dimensional CAD drawings depicting floor plans, sections, and views. BIM, in contrast, relies on digital three-dimensional building models based on an object-oriented modeling paradigm including semantics, descriptive data, and relationships of building elements. This holistic building modeling ap- proach also impacts the surveying workflow for building measurement as well as the data processing. Nevertheless, the basis for building measurement are geodetic surveying techniques with single-point methods (manual surveying, tacheometry) or aerial measurement methods (photogrammetry, laser scanning) in combination with appropriate surveying software. Also, new developments in context of spatial data capturing (UAVs, multi sensor and mobile mapping systems) rely on these basic methods. 26.1 Introduction Building measurement or, in general terms, building surveying, is a crucial factor for the creation of geometrically accurate building models. The aim of building sur- veying is to capture the current three-dimensional geometric conditions of existing buildings and to document them – nowadays almost always digitally – in draw- ings, plans, and models. The results typically consist of floor plans, sections, views J¨ org Blankenbach RWTH Aachen, Geod¨ atisches Institut und Lehrstuhl f¨ ur Bauinformatik & Geoinformationssys- teme, Mies-von-der-Rohe-Str. 1, 52074 Aachen, Germany e-mail: blankenbach@gia.rwth-aachen.de * assisted by Dr.-Ing. R. Schwermann, RWTH Aachen as well as MSc. S. Siebert (Aibotix GmbH) (Section 26.5.4) 1 In: Borrmann, A.; König, M.; Koch, C.; Beetz, J. (Eds): Building Information Modeling - Technology Foundations and Industry Practice, Springer, 2018, DOI: 10.1007/978-3-319-92862-3