Abstract
Building information modeling (BIM) has received significant research attention in the field of built heritage. As-built BIM refers to a BIM representation of the “as-is” conditions of built heritage at the time of a survey. Determining the level of development (LoD) is crucial for as-built BIM owing to its relevance to model effects and modeling efforts. This study addresses this issue from the viewpoint of a brick structure based on a case study of a fifteenth-century ruin in Nanjing, China. Three LoDs are proposed based on the combined use of a commercial platform and auxiliary tools: A host model linked with raster images composed using orthoimage and relief maps (LoD 1), an as-built volume with semantic skins (LoD 2), and a brick-by-brick model with custom industry foundation class parameters at local areas (LoD 3). The results reveal that LoD 1 caters to an efficient web-based workflow for brick-damage annotations; as-built dimensions can be extracted from LoD 2; and LoD 3 enables attributes, such as damage types, to be attached at the brick level. In future studies, the detection of brick shapes is expected to automate the process of as-built surface mapping.
Highlights
Bricks are among the oldest building materials, and brick-built heritage structures are widely distributed globally [1]
The file size of the level of development (LoD) 1 model without the images was less than 4 MB; this increased to 21 MB when the 27 relief maps with resolutions in a range 0.5–2 cm/pixel were included
Three LoDs were proposed for the case study, which was a fifteenth-century UNESCO heritage site in China
Summary
Bricks are among the oldest building materials, and brick-built heritage structures are widely distributed globally [1]. Recent developments in optical sensors and computer vision (CV) algorithms have made it easier to measure brick structures. Terrestrial laser scanning (TLS) and photogrammetry are widely used for these measurements [2,3]. Certain surveyed spaces are too narrow to use TLS and photogrammetry; technologies such as mobile scanning [4] and spherical cameras [5] are being developed. Even though the accuracies of these methods are lower than those of previous methods, they ensure rapid in situ measurements and robust scene transition in narrow spaces, as the devices can be operated while walking
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