Caller Location Capture with PIDF-LO, Eircode, and What3words Fallback

Overview#

A call-taker should see a single, accuracy-ranked map pin within seconds of call connect, regardless of whether the caller can speak the address. Phone-derived PIDF-LO, AML SMS, Eircode, and What3words all converge into one displayed fix written straight to the canonical incident.

This module captures the caller's location at the PSAP using a fusion of sources: handset PIDF-LO from the i3 call leg, AML SMS pushed by mobile operating systems, Eircode lookup against the An Post ECAD dataset, What3words for off-grid fixes, and HELD acquisition. The fused fix is plotted on the operational map and written to the canonical incident store so the dispatch path inherits it without rekeying.

Last Reviewed: 2026-05-05 Last Updated: 2026-05-05

Key Features#

• PIDF-LO Ingestion from the i3 Call Leg: Parse handset-derived Presence Information Data Format Location Object payloads carried with the inbound emergency call so the first available fix appears as soon as the call connects.

• AML SMS Receiver: Accept Advanced Mobile Location SMS pushed by mobile operating systems and treat the high-accuracy GNSS fix as a peer source alongside the call-signalling location.

• Eircode Resolver with Cache: Resolve Irish national postcodes against the An Post ECAD dataset to coordinates and a routing key, with a local cache to keep call-taker latency low.

• What3words Fallback: Accept a three-word address from a caller who cannot give a street address and convert it to coordinates, useful for rural, coastal, and off-grid incidents.

• HELD Acquisition: Use HTTP-Enabled Location Delivery as a complementary acquisition path where the access network can return a location for the caller's device.

• Accuracy-Ranked Fusion: Combine all available sources into a single ranked fix so the call-taker sees one authoritative pin rather than competing markers.

• Single Write to the Canonical Incident: Persist the fused fix to the incident record once so downstream dispatch, mapping, and responder views inherit the same location without rekeying.

• Location Validation Before Routing: Run the captured fix through Location Validation so PSAP routing decisions use a coordinate that the routing layer has already accepted.

Use Cases#

• Mobile Caller in an Urban Area: PIDF-LO from the call leg and an AML SMS arrive within seconds, the fused pin lands on the operational map, and the call-taker confirms the address verbally.

• Rural Eircode-First Caller: A caller reads their Eircode, the resolver returns coordinates from the cached ECAD lookup, and the dispatcher sees the property location even when GNSS is weak.

• Off-Grid or Coastal Incident: A hill-walker, beach visitor, or marine caller reads a What3words address, which resolves to coordinates on the same fused map view.

• Caller Cannot Speak: AML SMS and PIDF-LO together provide a location even when the caller is silent or unable to describe their surroundings.

• Indoor or Multi-Storey Caller: HELD acquisition from the access network supplements handset GNSS where the device fix alone is not enough to confirm the building.

• Cross-Border or Roaming Caller: Multiple acquisition paths increase the chance that at least one source returns a usable fix when handset routing differs from the caller's actual location.

Integration#

• NG112 Call Handling Stack: Caller location capture aligns with the i3 call flow handled by the NENA i3 handler so PIDF-LO carried with the call leg is parsed in the same path as other emergency call signalling.

• Location Validation and Call Routing: The fused fix is validated through the Location Validation Function and used by the Emergency Call Routing Function so the routing layer sees a coordinate it has already accepted.

• Active Call Panel Map View: The fused, accuracy-ranked fix renders in the LocationFusionMap component inside the PSAP active call panel so the call-taker sees a single pin rather than competing markers.

• Canonical Incident Record: The final fused fix is written once to the incidents_core.location JSONB column so downstream dispatch and responder views read the same authoritative location.

• Unified Incident Timeline: Capture is recorded as an argus.location.captured event in the incident unified timeline using a CloudEvents 1.0 envelope, with the PIDF-LO carried in the event payload for audit and replay.

• Eircode and What3words Adapters: Eircode resolution and What3words lookup sit behind dedicated middleware adapters so commercial licence terms, caching, and rate limits are handled outside of the call-taker hot path.

Open Standards#

• PIDF-LO (RFC 4119 / RFC 5491): Presence Information Data Format Location Object as carried with the i3 emergency call leg.

• LoST (RFC 5222): Location-to-Service Translation used in the PSAP routing path that consumes the captured fix.

• HELD (RFC 5985): HTTP-Enabled Location Delivery as a complementary location acquisition path from the access network.

• AML (ETSI EN 17128): Advanced Mobile Location specification covering the handset-to-emergency-number SMS flow.

• GeoJSON (RFC 7946): geographic data format used internally to carry the fused fix between services and into the canonical incident record.

• WGS 84 / EPSG:4326: latitude and longitude coordinate reference system used for all captured and fused locations.

• Eircode (An Post ECAD): Irish national postcode dataset used for postcode-to-coordinate resolution, consumed under a commercial licence.

• What3words API: three-word geocoding service used as a caller-readable fallback, consumed under a commercial licence.

• ETSI TS 103 479: NG112 location-routing context that frames how captured location is used for call routing and handover.

• CloudEvents 1.0: envelope used to record the location capture event on the incident unified timeline.