Engineer's Five-Test Study Finds Splines Offer No Storage or Search Advantage Over Polylines

A software engineer conducted five independent benchmarks to test whether cubic B-splines could outperform polyline representations for storing and searching GPS trajectory data. Initial results appeared to favour polylines, but an early flaw was uncovered: the spline fitting routine only verified accuracy at sampled points, allowing errors to drift as far as 110 metres between samples on 82% of tracks. After fixing the fitting method and preprocessing 200 GeoLife tracks into 585 clean trips, spline search recall improved significantly but still lagged behind Douglas-Peucker polylines across all tested tolerances. On synthetic smooth road data, splines showed a modest 22% compactness gain over time-aware polylines at very tight tolerances, though the advantage remained narrow and inconclusive. All code, benchmark reports, and decision logs have been published openly on GitHub and Zenodo for independent review.