An Automated and Efficient Slope Unit Division Method Coupled with Computer Graphics and Hydrological Principles  
[PERSON]  
1 School of Geosciences and Info-Physics, Central South University, 932 Lushan South Road, Changsha 410083, China; [EMAIL_ADDRESS] (T.X. ); [EMAIL_ADDRESS] (L.Z. )1 School of Civil Engineering, Yantai University, Yantai 264005, China; [EMAIL_ADDRESS] ([EMAIL_ADDRESS] [EMAIL_ADDRESS]. through increased landslide occurrences and other associated geohazards [1; 2; 3; 4; 5; 6]. According to official statistics from China's Ministry of Emergency Management, annual direct economic losses attributed to landslides exceed USD 70 million, with over 100 fatalities recorded annually. The \"Decision of the State Council on Strengthening Geological Disaster Prevention and Control\" mandates that scientifically validated risk assessment systems constitute a critical technical foundation for implementing the national \"community-based monitoring and prevention\" policy. Given their fundamental role in risk evaluation [7; 8; 9; 10; 11; 12], the methodological development of slope units [13; 14; 15] directly influences the precision of disaster early warning systems [3; 16; 17]. Therefore, innovative approaches achieving fine-grained resolution, full automation, and operational efficiency in slope unit delineation represent vital research directions. Two principal paradigms dominate existing automated slope unit classification approaches based on digital elevation models (DEMs) [18; 19; 20; 21; 22]: the hydrological analysis methodology [23; 24] and the unit homogeneity principle [25; 26]. The hydrological analysis approach employs watershed extraction techniques to construct closed drainage basins. Notably, [PERSON] et al. [27] developed a bidirectional DEM processing framework that integrates flow direction and flow volume parameters through forward and backward watershed analyses to establish slope units based on the hydrological process analysis method (HPAM). Extending this paradigm, [PERSON] et al. [28] incorporated topographic curvature characteristics by deriving concave-convex terrain elements from curvature analysis, proposing a curvature watershed method for slope partitioning. Although these methods demonstrate operational simplicity, they exhibit critical limitations, including (1) dependency on expert-driven manual corrections and (2) significant intra-unit mechanical parameter heterogeneity. The unit homogeneity principle posits that slope units should exhibit spatially consistent mechanical properties to satisfy the computational requirements of landslide stability analysis. [PERSON] et al. [29; 30] applied this principle by incorporating area and aspect control parameters, iteratively subdividing sub-watersheds obtained through flow accumulation analysis until user-defined threshold conditions were met. [PERSON] et al. [31; 32] redefined slope units as three-dimensional coherent, homogeneous, and closed regions by developing a hybrid methodology that combines morphological segmentation with aspect-slope homogeneity principles. Their approach involved both algorithmic automation and manual threshold adjustments. [PERSON] et al. [33] further advanced this paradigm through multi-scale segmentation algorithms that utilize slope and aspect inputs, achieving intra-unit consistency required for evaluation units. While these homogeneity-oriented methods enhance parameter uniformity, they neglect the hydrological processes' regulatory role in landslide genesis, leading to systematic discrepancies between evaluation models and actual hydro-mechanical coupling mechanisms. To address these methodological gaps, this research proposes an integrative framework that combines computer graphics algorithms [34; 35; 36] with hydro-mechanical principles.