ICSBS 2019 Semantic enrichment of city information models with LiDAR-based rooftop albedo 26 October 2019 Xue, F.*, Lu, W., Tan, T., & Chen, K., Assistant Professor Dept. of REC / iLab FoA, HKU, HKSAR, PRC Outline 1 Background 2 Semantic Enrichment using LiDAR 3 Discussion F. Xue: CIM with rooftop albedo 2 Section 1 BACKGROUND F. Xue: CIM with rooftop albedo 3 1.1 Background  Global urbanization  By 2050, 65% world’s population will live in cities (WHO, 2015)  Irreversible; Even faster in China  Leads to urban vulnerability (a.k.a. ‘city diseases’)  ‘Dead’ space/landscape, low familiarity with surroundings,  Poor waste treatment, environment (air, water) pollution, China’s and global urbanization rates source: gov.cn  Heritage destruction, aging town blocks, inefficient traffic,  Disasters (earthquake, climate change), resource crisis, …  Demands smarter and more resilient development  (a) Smarter analysis and decisions in multiple disciplines  (b) On basis of accurate, timely urban semantics F. Xue: CIM with rooftop albedo Global urban vulnerability level (Birkmann et al, 2016) source: nature.com 4 1.2 Urban semantics  Why semantics from signals? (Rowley & Hartley, 2017)  Answering interrogative questions (what, who, where, when)  Enabling automated reasoning / checking  Abstracted, processed from data and signals Data: Digital pixels (0~255 R, G, B)  Types of urban semantics  Geometric: Dimension, location, rotation, color, …  Non-geometric facts: Function, materials, history, owner, …  Instructions (how-to): Manufacturing, installation, access, …  Common databases / interfaces  BIM/CIM: building/city information model  GIS: geographic information system F. Xue: CIM with rooftop albedo Semantics: Car, building, tree, … 5 1.3 Roofs  Considerable in typical metropolises  20~25% urban surfaces (Rose et al. 2003)  Rooftop albedo  Reflected (other than absorbed) solar radiation by coatings o  Negative radiative forcing “Cool” roofs (Source: Lawrence Berkeley Laboratory)  At a worldwide level, every year (Akbari et al. 2009) o Offsets billions of tons of CO₂ emissions o billions of dollars of energy bills  Became mandated in certain areas o E.g., California Energy Commission (2005)  Problems in CIM roofs  No albedo, even not accurate in 3D F. Xue: CIM with rooftop albedo 2.5D “block” city map Radiative forcing (Source: Wikipedia) 6 1.4 Opportunity and aims  LiDAR data (infrared laser)  Light Detection and Ranging o Different devices: total station, vehicle-borne, drone  Aerial LiDAR from drones / fixed-wing aircraft o Large-scale o Uniform point density (4~1,000 pts/m2) o Laser reflectance (almost linear to albedo) (Levinson et al. 2014) Illustration of aerial LiDAR o Rooftop details  Semantic enrichment using LiDAR ?  Geometry  Non-geometric, e.g., albedo, green roof  topology F. Xue: CIM with rooftop albedo Infrared laser reflectance (warmer color = less received) 7 Section 2 SEMANTIC ENRICHMENT USING LIDAR F. Xue: CIM with rooftop albedo 8 2.1 Semantic enrichment: Geometry  LiDAR  RANSAC  rectification  LoD2 model (Chen et al. 2018) F. Xue: CIM with rooftop albedo 9 2.2 Semantic enrichment: Rooftop albedo (a) (b) F. Xue: CIM with rooftop albedo 10 2.2 Semantic enrichment: Green roofs prediction  Geometry + albedo  material prediction, e.g., green roofs (Tan et al. 2019) F. Xue: CIM with rooftop albedo 11 2.3 Semantic enrichment: Symmetry  3D point cloud  symmetry hierarchy (Xue et al., 2019)  Time = 98.6s  A knowledge discovery tool for further 3D modeling  PCR = 93.7% F. Xue: CIM with rooftop albedo 12 Section 3 DISCUSSION F. Xue: CIM with rooftop albedo 13 F. Xue: CIM with rooftop albedo 14 3.1 Discussion  A pilot study of rooftop albedo and materials prediction  From LiDAR point clouds o Using geometric features (from LiDAR) o Using laser reflectance (from LiDAR)  For smart city applications o Simulations, heat island, micro climate, etc.  Limitations  A small-scale test  No benchmarking against other methods  In terms of excessive heat on roofs / micro climate  Which is the best, green roof, PV panel, or simple white paint …?  “One size fits all ?” What are the trade-off ? F. Xue: CIM with rooftop albedo 15 References  Akbari, H., Menon, S. & Rosenfeld, A. 2009. Global cooling: Increasing world-wide urban albedos to offset CO2. Climatic Change, 94(3-4): 275-286. doi:10.1007/s10584-008-9515-9  Birkmann, J., Welle, T., Solecki, W., Lwasa, S., & Garschagen, M. (2016). Boost resilience of small and mid-sized cities. Nature News, 537(7622), 605.  California Energy Commission. 2005. California Energy Commission Building Energy Efficiency Standards, For Residential and Nonresidential. Publication No. CEC-400-2006-015. Sacramento, CA, USA: California Energy Commission.  Chen, K., Lu, W., Xue, F., Tang, P., & Li, L. H. (2018). Automatic building information model reconstruction in highdensity urban areas: Augmenting multi-source data with architectural knowledge. Automation in Construction, 93, 2234.  Levinson, R., Chen, S., Berdahl, P., Rosado, P. & Medina, L. A. 2014. Reflectometer measurement of roofing aggregate albedo. Solar Energy, 100: 159-171. doi:10.1016/j.solener.2013.11.006  Rose, L. S., Akbari, H. & Taha, H. 2003. Characterizing the fabric of the urban environment: a case study of Greater Houston, Texas. Berkeley, CA, USA: Lawrence Berkeley National Laboratory.  Rowley, J., & Hartley, R. (2017). Organizing knowledge: an introduction to managing access to information. Routledge.  Tan, T., Chen, K., Lu, W., & Xue, F. (2019). Semantic Enrichment for Rooftop Modeling using Aerial LiDAR Reflectance. In Proceedings of the 2019 IEEE International Conference on Signal Processing, Communications and Computing.  World Health Organization. (2015). Global Report on Urban Health—Executive Summary. http://www.who.int/kobe_centre/measuring/urban-global-report/en/  Xue, F., Chen, K., & Lu, W. (2019). Architectural symmetry detection from 3D urban point clouds: A derivative-free optimization (DFO) approach. In Advances in Informatics and Computing in Civil and Construction Engineering (pp. 513519). Springer, Cham. F. Xue: CIM with rooftop albedo 16 Thank you ! Q&A time 17