Location and orientation united graph comparison for topographic point cloud change estimation

3D topographic point cloud change estimation produces fundamental inputs for understanding Earth surface process dynamics. In general, change estimation aims at detecting the largest possible number of points with significance (i.e., difference $>$ uncertainty) and quantifying multiple types of topographic changes. However, several complex factors, including the inhomogeneous nature of point cloud data, the high uncertainty in positional changes, and the different types of quantifying difference, pose challenges for the reliable detection and quantification of 3D topographic changes. To address these limitations, the paper proposes a graph comparison-based method to estimate 3D topographic change from point clouds. First, a graph with both location and orientation representation is designed to aggregate local neighbors of topographic point clouds against the disordered and unstructured data nature. Second, the corresponding graphs between two topographic point clouds are identified and compared to quantify the differences and associated uncertainties in both location and orientation features. Particularly, the proposed method unites the significant changes derived from both features (i.e., location and orientation) and captures the location difference (i.e., distance) and the orientation difference (i.e., rotation) for each point with significant change. We tested the proposed method in a mountain region (Sellrain, Tyrol, Austria) covered by three airborne laser scanning point cloud pairs with different point densities and complex topographic changes at intervals of four, six, and ten years. Our method detected significant changes in 91.39 % − 93.03 % of the study area, while a state-of-the-art method (i.e., Multiscale Model-to-Model Cloud Comparison, M3C2) identified 36.81 % − 47.41 % significant changes for the same area. Especially for unchanged building roofs, our method measured lower change magnitudes than M3C2. Looking at the case of shallow landslides, our method identified 84 out of a total of 88 reference landslides by analysing change in distance or rotation. Therefore, our method not only detects a large number of significant changes but also quantifies two types of topographic changes (i.e., distance and rotation), and is more robust against registration errors. It shows large potential for estimation and interpretation of topographic changes in natural environments.