Calculation of bloodstain impact angles using an Active Bloodstain Shape Model

摘要

Objectives: Traditional Bloodstain Pattern Analysis (BPA) estimates impact angles for bloodstain spatters by employing ellipses and an inverse sine. This approach is based upon a simplification of the stain formation process, and ignores the physical properties of blood, and its intricate interactions with the target surface. This research presents a data-driven approach, starting from experimental bloodstain spatters. No assumptions about the shape of stains or about the relation between the shape and their impact angle are made a priori. Materials and methods: Experimental bloodstain data is gathered, after which shape variations are extracted by employing an Active Shape Model. A non-linear regression is then used to explain the relation between stain shape and impact angle. Results: Experimental results show that traditional width-length ratios may deviate from the assumed inverse sine. The proposed approach, on the other hand, closely follows the experimental data through its regression. Additional experiments have shown an increased accuracy on impact angle estimates for the proposed approach when compared to automatic ellipse fitting. Conclusion: The proposed method performs better than automatic ellipse fitting. The higher accuracy and faster and more objective analysis suggest that the developed model is applicable in real-life scenarios, and can provide a valuable update to Bloodstain Pattern Analysis.