Online vs Offline Map Matching Trade-offs

Online Map Matching

Processes GPS points as they arrive in real-time. Each new point updates the current match. Used for live navigation and tracking. Latency must be low: process point and return match within 100 milliseconds.

Online matching has limited context. It sees only past points, not future ones. When approaching an ambiguous intersection, it cannot know which way the vehicle will turn. May need to retroactively correct earlier matches when new evidence arrives.

Offline Map Matching

Processes complete GPS trace after the trip ends. Sees all points before matching. Can use future points to disambiguate past positions. A point near an intersection matches better when we know which road comes next.

Offline matching produces better accuracy. It considers the entire path globally. Forward-backward algorithms (like Viterbi on HMM) find the most likely complete path. Used for billing, analytics, and post-trip reports where accuracy matters more than latency.

Hybrid Approaches

Use online matching for live display. Re-run offline matching after trip completes for billing and analytics. The online match shows the driver on a road immediately. The offline match corrects any errors for the final record.

Buffered online: accumulate 5-10 seconds of points before matching. Slight delay but better accuracy than pure online. Acceptable for navigation where 5-second lag is not noticeable.