1. 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

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

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

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

5. 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. 

6. 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.

7. 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.

8. 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

9. Phase shift method

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

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

12. 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

13. Selecting a part and previewing

14. Slope compensation of striation mark

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

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

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

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

19. Tablets and stamps
Toolmark investigation

20. 3D measurement

21. 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° mm

22. translations
pacman-holder

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

24. Example occlusion

25. Angle of holder with system
Preventing occlusion
Angle of holder with system

26. 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

27. Questions ??