An airsoft projectile strikes the eye of a person wearing protective goggles. The incident appears to be a fortuitous accident, but the defense claims the shot was accidental. To resolve the discrepancy, a forensic team turned to 3D reconstruction. Using photogrammetry and ballistic simulation, they managed to trace the exact trajectory of the projectile, including an unexpected ricochet that changed the direction of the impact.
Forensic Pipeline: From Point Cloud to Ballistic Simulation 🎯
The workflow began with scene capture using photogrammetry in Agisoft Metashape. Multiple photographs were taken of the protective goggles, the injured person's position, and the immediate surroundings to generate a high-resolution 3D model. This model was exported to MeshLab for mesh cleaning, removing noise and artifacts from the capture. Finally, the cleaned model was imported into Maya. There, the projectile was recreated and rigid body dynamics were applied to simulate the ballistic trajectory. The analysis in Maya revealed that the projectile did not impact directly, but instead ricocheted off the lower edge of the goggle frame before deflecting towards the eye.
Hypothesis Validation and the Value of Simulation 🔍
The simulation demonstrated that the original impact angle was too low to reach the eye without the ricochet. This finding contradicted the shooter's version, who claimed to have fired upwards. The forensic reconstruction not only confirmed the mechanics of the accident but also allowed calculating the exact height of the barrel at the moment of the shot. The use of this pipeline turns subjective testimony into quantifiable visual evidence, essential for determining responsibility in injury crimes.
As can be differentiated through ballistic simulation and 3D morphometry between a direct impact on the lens of the protective goggles and a deflection of the projectile entering through the edge or side slit without breaking the glass.
(PS: In the forensic pipeline, the most important thing is not to mix the evidence with the reference models... or you'll end up with a ghost in the scene.) 👻