Using 3DF Zephyr to determine body-worn camera position

Photogrammetry has been used consistently in forensic settings to document crime scenes three-dimensionally. Traditionally, a large number of still photos are taken, and information from those photos is used to create a three-dimensional (3D) model. This research aimed to determine how accurately 3DF Zephyr, a photogrammetry software, could calculate the position of a body-worn camera through recorded video. In 3DF Zephyr, frames are extracted at regular intervals from the video to create a 3D model. Videos were taken with the Axon Body 3, Body 2, and Flex 2 body-worn cameras, five trials per camera, and five measurements per trial. A 3D reconstruction of a mock scene was created from each body-worn camera with 3DF Zephyr. A FARO laser scanner was used to obtain ground truth data. Coordinates of the camera positions were recorded and compared to ground truth coordinates. The Axon Body 3, Axon Body 2, and Axon Flex 2 had average errors of 7.6 cm, 10.1 cm, and 9.5 cm, respectively. The total average error for all cameras was 9.1 cm with a standard deviation (σ) of 4.8 cm. Thus, it is possible to estimate camera position within a 24 cm radius circle, accounting for 98.7% of all errors. Estimating camera position allows an officer's position to be pinpointed within that circle. This technique can be used to corroborate witness testimony in officer-shooting incidents. This study's results may be limited, as accuracy can decrease under excessively low-light or low-texture conditions.