CGAL’s 3D Alpha Wrap robustly produces valid enclosing meshes for defective input using two parameters: α, which controls the carving-ball size, and δ, an offset that controls the distance between the input and the output surface vertices. However, preserving sharp concave features often requires a small global α-value, which also increases refinement in regions where additional vertices do not substantially improve the approximation. This paper proposes a 𝜏-guided extension that adds a local face-to-input distance criterion to the original algorithm. The new parameter 𝜏 triggers additional refinement only where the current wrap remains locally too far from the input.

To make this refinement effective near concave features, we introduce R3 as an additional vertex-insertion strategy alongside the two insertion strategies of the original algorithm. R3 aims to place new vertices more directly near sharp concave features, whereas the original two insertion strategies may reach comparable vertex positions only after repeated refinement. The extension preserves the carving-based structure of the original algorithm, and we prove that the guarantees of termination, strict enclosure, watertightness, and manifoldness still hold. Experiments on 3D BAG building data show that the proposed method improves both average and local approximation quality, achieving lower directed Chamfer distances with fewer output faces than the original algorithm. Although R3 is less time efficient per insertion, it places vertices more effectively near concave features, so fewer insertions are needed to reach lower approximation errors. As a result, the proposed method can reduce runtime in the tested use case. ... Read more

To help prevent flooding of rivers and cities, Dutch maritime contractor Van Oord regularly dredged 52 side channels as part of the Dutch Department of Waterways and Public Works' (Rijkswaterstaat) "Room for Rivers" strategy. Side channels make rivers more resilient to flooding by providing increased flow capacity, buffer space, and a secondary path downstream for water. Van Oord wishes to know how they can better leverage their growing historical data collection to enable predictive maintenance of side channels in the form of dredging.
Instead of developing a complex hydrological model, which would require deep knowledge of river morphology. We, as Geomatics students, extracted insights directly from the available geospatial data. For our 10-week MSc Geomatics Synthesis Project, our main research question is as follows: "How can the features of a side channel be identified and extracted to enable predictive maintenance?"
In order to answer this question for our client Van Oord, we performed a literature review and interviewed domain experts to identify relevant characteristics of side channels. Then, we explored the available geo-spatial data to determine which characteristics can be modeled as features, before processing the data in an FME pipeline to calculate these feature values in an automated, extendible, and understandable way. These features were then stored in a geo-spatial database. Reading from this database, we created a prototype machine learning model that takes the features as input. The model enables analysis of the side channels to derive insights into the sedimentation of side channels, reaching 84% accuracy within a 5cm error for the Bakenhof channel.

The result is a robust FME-based data processing pipeline, a geo-spatial database with 19 unique features for 26 suitable side channels, and a prototype neural network showing significant predictive ability. The product enables the client to better estimate side channel behavior, enabling informed predictive maintenance, as well as allowing the client to better decide moments when expensive channel measurements can be skipped. ... Read more