Data taking and quality control for complex surveys: Case study Sagrada Familia

Abstract

This article proposes a methodology to make the survey of complex and high buildings, with the Antoni Gaudi’s Sagrada Familia (Fachada del Nacimiento) as case of study, with high resolution Topography, Terrain Laser Scanner (TLS) and Photogrammetry technology. An architectural survey of huge complexity due to the difficulty on the data taking and the volume of the recorded data, considering the height (107 m), the incidence angle and the self-occlusions; the geometric complexity of the façade, and the needs of a resolution, precision and covering higher than 95% of the heritage building, that allows the detection of pathologies in restauration processes. The TLS survey was made using different kind of equipment, tripods with telescopic arms, a telescopic pole of 8 m and lift platforms of 16, 20 and 26 m high; with more than 4530 TLS positions, all related to each other. The photogrammetry survey was made with cranes and stabilizing systems. These solutions require of some quality controls during the taking data with sensors and while processing the data [1], validating every position, the alignment between them and during the photogrammetry process. Obtaining in this controls an average statistical error less than 7 mm, comparing the support high resolution topographical network to the TLS model and the photogrammetric orthophoto. With this methodology, some useful products for restoration works are obtained, achieving such high resolution that pathologies can be detected anywhere in the building; even creating material to study the top of the towers at 107 m high with the information validated from topography, TLS and photogrammetry.