An off-line navigation of a geometry PIG using a modified nonlinear fixed-interval smoothing filter

In this paper, a modified nonlinear fixed-interval smoothing filter is proposed for an off-line Strapdown Inertial Navigation System (SDINS) suitable for a geometry Pipeline Inspection Gauge (PIG). The proposed smoothing filter has a two-filter structure and a modified propagation and update equation for the backward filter. A complete smoothing algorithm with the modified backward filter is successfully applied to the geometry PIG developed by Korea Gas Company and Seoul National University, demonstrating that the proposed smoothing filter provides accurate navigation data in a harsh physical environment.