SCAIM Seminar: Luis Zarrabeitia

  • Date: 09/13/2011
  • Time: 12:30
Luis Zarrabeitia

University of British Columbia


Extracting 3D blood flight trajectories from videos for forensic analysis



At present, blood stain pattern analysis (BPA) is a largely qualitative
sub-discipline of forensic science. Our ultimate aim is to develop
software for quantitative analysis to aid BPA forensic analysts. Towards
this end, we are developing a sound physics-based model (i.e,
incorporating gravity and air resistance) for bloodstain pattern
formation using pre-recorded videos of simulated blood-letting events.
The simulations consist of fake blood encased in ballistic gel being
splattered by projectiles. The resulting blood flight trajectories are
recorded by a high speed camera.

We present a method for extracting the three-dimensional flight
trajectories of liquid droplets from video data. A high-speed stereo
camera pair records videos of experimental reconstructions of projectile
impacts and ensuing droplet scattering. After background removal and
segmentation of individual droplets in each video frame, we introduce a
model-based matching technique to accumulate image paths for individual
droplets. Our motion detection algorithm is designed to deal gracefully
with the lack of feature points, with the similarity of droplets in
shape, size, and color, and with incomplete droplet paths due to noise,
occlusions, etc. The final reconstruction algorithm pairs
two-dimensional paths accumulated from each of the two cameras’ videos
to reconstruct trajectories in three dimensions.

Traditional forensic methods for reconstructing crime scenes, such as
“stringing”, ignore the effects of gravity and drag. Our preliminary
results show that gravity and drag play an important role in the
trajectories of the droplets. The reconstructed droplet trajectories
constitute a starting point for a physically accurate model of blood
droplet flight for forensic bloodstain pattern analysis.

This is joint work with Dhavide Aruliah and Faisal Qureshi, based on
experiments by Raquel Murray, Paul Prior and Franco Gaspari.

Other Information: 

Location: WMAX 110


For more information please visit UBC SCAIM department