High speed in-line holography is used by our laboratory for many years to visualize the glass fibers being drawn out in different manufacturing process. The knowledge of thin fiber trajectories (which materialize flow lines) is of a great interest, but the human-based analysis of holograms is a tedious work. Consequently, an automated holographic trajectography is required. Because of the turbulence and the temperature variations which induce high gradients of the refraction index, the holograms present an important optical noise. This necessitates new approaches in image processing : high resolution image rotation, analysis with a rectangular window, intensity subtraction between a focused image and a defocused image. Our automatic reconstructing system executes mainly the following stages : a) image focusing procedure, b) optical and numerical filtering, c) detection of an 1-D object and determination of its angular position, d) driving the x, y translations. In this paper, we describe the previous optical and numerical methods and report on the preliminary results.