Learning from synthetic point cloud data for historical buildings semantic segmentation

Historical heritage is demanding robust pipelines for obtaining Heritage Building Information Modeling models that are fully interoperable and rich in their informative content. The definition of efficient Scan-to-BIM workflows represent a very important step toward a more efficient management of the historical real estate, as creating structured three-dimensional (3D) models from point clouds is complex and time-consuming. In this scenario, semantic segmentation of 3D Point Clouds is gaining more and more attention, since it might help to automatically recognize historical architectural elements. The way paved by recent Deep Learning approaches proved to provide reliable and affordable degrees of automation in other contexts, as road scenes understanding. However, semantic segmentation is particularly challenging in historical and classical architecture, due to the shapes complexity and the limited repeatability of elements across different buildings, which makes it difficult to define common patterns within the same class of elements. Furthermore, as Deep Learning models requires a considerably large amount of annotated data to be trained and tuned to properly handle unseen scenes, the lack of (big) publicly available annotated point clouds in the historical building domain is a huge problem, which in fact blocks the research in this direction. However, creating a critical mass of annotated point clouds by manual annotation is very time-consuming and impractical. To tackle this issue, in this work we explore the idea of leveraging synthetic point cloud data to train Deep Learning models to perform semantic segmentation of point clouds obtained via Terrestrial Laser Scanning. The aim is to provide a first assessment of the use of synthetic data to drive Deep Learning--based semantic segmentation in the context of historical buildings. To achieve this purpose, we present an improved version of the Dynamic Graph CNN (DGCNN) named RadDGCNN. The main improvement consists on exploiting the radius distance. In our experiments, we evaluate the trained models on synthetic dataset (publicly available) about two different historical buildings: the Ducal Palace in Urbino, Italy, and Palazzo Ferretti in Ancona, Italy. RadDGCNN yields good results, demonstrating improved segmentation performances on the TLS real datasets.