Geofencing

A geofence is defined as a virtual polygon or radius around a set of geographic coordinates. In cold chain logistics, boundaries are typically drawn around warehouses, distribution centers, cross-docking facilities, and hospital loading bays. The geometry can be a simple circle (point-radius) or a complex polygon matching the exact footprint of a facility. Precision matters: a poorly drawn polygon that includes a public road may trigger false entry events when non-relevant vehicles pass by. Advanced systems support 3D geofences that incorporate altitude for multi-story facilities or drone corridors.

Geofencing systems fire automated actions based on discrete spatial events. The three primary triggers are:

• Entry: A tracked asset crosses from outside to inside the virtual perimeter.
• Exit: The asset leaves the defined boundary.
• Dwell: The asset remains stationary within the boundary for a configurable duration.

In cold chain monitoring, a dwell trigger at a cross-dock can automatically start a timer. If the shipment hasn't departed within a specified window, an escalation alert is sent to prevent cold chain breaks from prolonged staging in uncontrolled environments.

Geofencing accuracy depends entirely on the underlying positioning technology. Common layers include:

• GNSS (GPS, GLONASS, Galileo): Provides global outdoor positioning with 3-10 meter accuracy.
• RTLS (Real-Time Location Systems): Uses Active RFID, Ultra-Wideband (UWB), or Bluetooth Low Energy (BLE) beacons for sub-meter indoor positioning where satellite signals fail.
• Cell Tower Triangulation: A fallback for coarse location when GPS is unavailable.
• Wi-Fi Positioning: Uses known access point locations for urban and indoor fixes.

A robust cold chain system fuses multiple sources to maintain in-transit visibility even when shipments move through GPS-denied environments like refrigerated holding areas.

Individual geofences can be linked into logical sequences that mirror a planned route. A shipment moving from a manufacturing plant to a distribution center and then to a hospital passes through a chain of geofences. The system expects entry and exit events in a specific order. A corridor geofence is a linear polygon drawn along a prescribed highway or shipping lane. Deviations from the corridor trigger route deviation alerts, indicating potential theft, hijacking, or unauthorized stops that could compromise cold chain compliance under GDP regulations.

The core value of geofencing is hands-free orchestration. When a trigger fires, the system executes predefined actions:

• Push notification to a logistics manager's device.
• Webhook call to an external system (ERP, WMS) to update shipment status.
• API-triggered command sent to an IoT data logger to increase its reporting frequency.
• Automated email to a receiving pharmacy with an updated estimated time of arrival.

This event-driven architecture eliminates manual check-calls and enables autonomous supply chain responses to spatial events in real time.

Advanced geofencing combines spatial boundaries with temporal constraints. A rule might state: 'If a shipment containing mRNA vaccines dwells at an unplanned location for more than 15 minutes between 10:00 and 16:00 UTC, trigger a critical excursion management alert.' This geo-temporal logic prevents false alarms from brief, harmless stops while catching genuine risks. The system can also enforce curfew compliance, ensuring high-value pharmaceutical shipments only move during authorized hours and remain within secured geofenced yards overnight.