A 3D scanning based image processing technique for measuring the sequence of intersecting lines

The determination of the sequence of two intersecting lines is still an ongoing and important issue in questioned document examination. In literature, scanning electron microscopy, optical profilometry, laser profilometry, and video reflectance spectroscopy were used for analyzing the intersecting lines. In this study, a cheap and easy-to-operate 3D scanner was used to study this problem. Intersections of homogenous and heterogeneous strokes were drawn using different brands of 1.0 mm blue, black, and red ballpoint pens on conventional printing paper, i.e., 80 g/m^2, and uncoated A4 white paper by two different handwriting examiners. The analysis of the 3D surface of the crossing lines shows that the bottom of the profile of the first line has a considerable trough, while the second line has comparably smaller fluctuations. The 3D scan analysis is not affected by the brands and colors of the pen and is independent of the substrate and the number of sheets lying underneath the paper. The effect of the pen pressure shows that if the pressure of the second line is less than the first one, the sequence determination becomes harder and sometimes impossible. As these cases can be eliminated before the 3D scan, the developed method is sensitive, cheap, and easy to operate.