AAFS 2004 Dallas Zeno Geradts zeno@holmes.nl The Use of 3D Acquisition Techniques of Surfaces for Forensic Image Databases AAFS 2004 Dallas Zeno Geradts zeno@holmes.nl

Outline Introduction Methods Results with Toolmarks Results with Drug pills Conclusion and discussion

Methods - Stereo Photogrammetry - Laser Scanning Triangulation - Moiré Fringe Contouring - Structured light

Triangulation 1 2 3 4 5 2’ 3’ 4’ 5’ x z   CCD-camera lichtbundel 1’

Stereo Photogrammetry combining two (or more) images from cameras with a different viewpoint. similar in the way that we see depth with two eyes. An algorithm and computer can exploit this offset to perform the same operation. 

Laser Scanning involves projecting a stripe of laser light onto the object of interest and viewing it from a camera. The stripe is then scanned across (or around) the scene to produce 3D data for the rest of the object.

Moiré Fringe a grating is projected onto an object and an image is formed in the plane of some reference grating. The image then interferes with the reference grating to form Moiré fringe contour patterns which appear as dark and light stripes. Analysis of the patterns.

Structured Light patterns of light (grids, stripes, elliptical patterns etc.) are projected onto an object. Surface shapes are then deduced from the distortions of the patterns that are produced on surface of the object. With knowledge of relevant camera and projector geometry, depth can be calculated by triangulation

Phase shift method

Phase-code combination method graycode High resolution phase shift Zrel(x,y) = ((x,y) * hmin)/ 2)

Projection system Digital Mirror Device matrix met 600x800 mirrors On/off in 20 sec

Research project Toolmarks Continuation of Previous research in 1995 for side light User interactive signature selection Calculating the standard deviation of the difference after normalization steps

Selecting a part and previewing

Slope compensation of striation mark

Slope in z-direction Compensate by selecting the edges and normalize

Experiment 6 screwdrivers Striation marks of 45 degrees to the surface Both gray values / 3D values

Conclusion Higher correlation factors Less sensitive to the lighting of the surface

Research project XTC tablets Use of 3D equipment in XTC-investigation Comparison stamp / tablet

Tablets and stamps Toolmark investigation

3D measurement

Side view 50 -50 -100 -150 -200 -250 -300 -350 -400 m -450 418 m -50 -100 -150 -200 -250 -300 -350 -400 -450 m 418 m 112.9° 0 1 2 3 4 5 6 mm

translations pacman-holder

occlusion Triangulation angle:  = 30° Not all angles are possible = 60 º CCD - camera Light source Sample ccd light source Triangulation angle:  = 30° Not all angles are possible Combining images Use of special pacman holder

Example occlusion

Angle of holder with system Preventing occlusion Angle of holder with system

Conclusions With the structured light technique, heights of 5 micron can be measured. The matching of the different positions is possible with the Fourier Mellin algorithm Structured light can be useful for filling databases in a higher resolution setting and prevention of occlusion

Questions ??