  A new method called Neighbor Cell Deposited Energy Ratio (NCDER) is proposed
to reconstruct incidence position in a single layer for a 3-dimensional imaging
electromagnetic calorimeter (ECAL).This method was applied to reconstruct the
ECAL test beam data for the Alpha Magnetic Spectrometer-02 (AMS-02). The
results show that this method can achieve an angular resolution of 7.36\pm 0.08
/ \sqrt(E) \oplus 0.28 \pm 0.02 degree in the determination of the photons
direction, which is much more precise than that obtained with the
commonly-adopted Center of Gravity(COG) method (8.4 \pm 0.1 /sqrt(E) \oplus
0.8\pm0.3 degree). Furthermore, since it uses only the properties of
electromagnetic showers, this new method could also be used for other type of
fine grain sampling calorimeters.
