AN ALGORITHM FOR AUTOMATIC-INDEXING OF OSCILLATION IMAGES USING FOURIER-ANALYSIS

A fast and reliable algorithm has been developed for auto-indexing osc illation images. The observed reflection positions are used to compute the corresponding reciprocal-lattice vectors assuming a stationary cr ystal. These vectors are then projected onto a chosen direction. The p rojections are subjected to a one-dimensional Fourier analysis. A larg e Fourier term will be found that has a periodicity corresponding to t he interplanar distance if the chosen direction happens to be perpendi cular to a set of widely separated reciprocal-lattice planes. Explorat ion of such directions over a hemisphere establishes the best potentia l basis vectors of the real cell. The program has successfully determi ned the lengths and directions of basis vectors for numerous unit cell s having cell dimensions ranging from 16 to 668 Angstrom and oscillati on ranges from 0.2 to 2.0 degrees.