Improved Method of the Extensive Air Shower Arrival Direction Estimation
  The properties of measuring systems of the Extensive Air Showers arrival directions (EAS goniometers), consisting of the set of spatially separated detectors registering the moments of EAS frontal passage, are considered. The advantage of volumetric goniometers in comparison with the commonly used flat ones is shown. The proper points selection method for detectors spatial arranging is suggested, providing the best accessible estimation accuracy within the given detectors number and installation overall dimensions 
M.S. Svanidze, Yu.G. Verbetsky