The streaming track state pattern reacts to tracks in real time — you get an execution on every detection update, letting you alert while conditions are still developing. The trade-off is higher processing volume and the need to manage event closure when conditions clear.
This guide uses zone intrusion as the running example (detecting objects in restricted zones), but the same pattern applies to any streaming track use case — loitering, speeding, dwell-time monitoring, and more.
What you’ll build
The workflow follows this structure:
- Trigger receives detection data from the state machine
- Type I Check evaluates zone thresholds (intersection, dwell time, velocity)
- Event Orchestrator routes based on check results — create event, no action, update event, or close event
- Create path captures a still image, creates the event, generates a GIF, and sends an email
- Close path closes the event with duration metadata
- Replay Trigger (disabled) is available for testing with historical data
Prerequisites
- A Worlds site with configured zones
- GraphQL Subscription API credentials in n8n
- SendGrid API credentials (for email alerts)
- The state machine running and connected to your n8n instance
Step 1: Detection Webhook Trigger
The trigger listens for detections across your cameras.
Configuration:
- Mode: Streaming
- Signal Type: Track State
- Site: Select your site
- Data Sources: Select the cameras you want to monitor
- Object Types: Select the object types to watch for (e.g., forklift, person, AMR)
The trigger receives every track_created, track_updated, and track_expired signal for matching detections. Each execution carries the full track state with position, velocity, zone data, and dwell times.
Add a Replay Trigger connected to the same downstream node and keep it disabled. This lets you test the workflow with historical data at any time without modifying the live workflow.
Step 2: Type I Check (Track in Zone)
The check node evaluates whether the detection meets your threshold criteria.
Configuration:
- Site: Same site as the trigger
- Threshold Groups: Create a group with:
- Zone IDs: Select the zones you want to monitor
- Intersection: Enable, operator
>=, value 10 (object must overlap zone by at least 10%)
- Dwell Time: Enable, operator
>=, value 300 (object must be in zone for 5+ minutes)
- Velocity: Enable, operator
<, value 5 (object must be moving slowly)
What happens: For each incoming track state, the node checks every configured zone. A zone passes if the track is present with >=10% intersection, has been there >=300 seconds, and is moving below 5 px/s. If at least one zone passes, the check passes.
Output: Adds checks.type1.passed (boolean) and checks.type1.matching_zones (array of zone IDs that passed) to the data.
Adapting thresholds for other use cases
| Use Case | Intersection | Dwell Time | Velocity |
|---|
| Obstruction / loitering | >= 10% | >= 300s | < 5 px/s |
| Zone intrusion | >= 5% | — (disabled) | — (disabled) |
| Speeding in zone | >= 10% | — (disabled) | > 50 px/s |
| Extended stop | >= 20% | >= 600s | < 1 px/s |
Step 3: Event Orchestrator
The orchestrator reads the Type I check results and decides what to do.
Configuration:
- Scope Type: track (one event per tracked object)
- Scope Expression:
={{$json.track_state.track_id}} (default)
- Logic Operator: AND
Routing:
| Output | Wired to | When |
|---|
| Create Event (0) | Image capture + Event Manager + GIF + Email | First time checks pass for this track |
| No Action (1) | Nothing | Checks don’t pass, no active event |
| Update Event (2) | Nothing (in this workflow) | Checks still pass, event already exists |
| Close Event (3) | Event Manager (close) | Checks no longer pass, event exists |
Step 4: Create Event path
When the orchestrator routes to “Create Event”:
4a. Capture still image
Node: Worlds Actions → Process Detection Image
| Parameter | Value |
|---|
| Track IDs | ={{$json.track_state.track_id}} |
| Timestamp | ={{$json.track_state.last_seen}} |
| Zone IDs | ={{$json.checks.type1.matching_zones[0]}} |
4b. Create event in Worlds
Node: Event Manager → Create Event
| Parameter | Value |
|---|
| Event Producer | Select your event producer |
| Event Type | Your event category (e.g., “Operational”, “Safety”) |
| Event Subtype | Descriptive name (e.g., “Obstruction Event”, “Zone Intrusion”) |
| Start Time | ={{$json.track_state.last_seen}} |
| Track IDs | ={{$json.track_state.track_id}} |
| Key | Value |
|---|
| trackId | ={{$json.track_state.track_id}} |
| dataSourceID | ={{$json.track_state.datasource_id}} |
| dataSourceName | ={{$json.track_state.datasource_name}} |
| tag | ={{$json.track_state.tag}} |
| position | =({{$json.track_state.position.geo.lat ?? 'NaN'}},{{$json.track_state.position.geo.lon ?? 'NaN'}}) |
| source | ={{$workflow.id}} |
4c. Generate GIF
Node: Worlds Actions → Process Detection Image → Create GIF
| Parameter | Value |
|---|
| Track IDs | ={{$json.track_state.track_id}} |
| Timestamp | ={{$json.track_state.last_seen}} |
4d. Send email alert
Node: Worlds Actions → Send Worlds Email
| Parameter | Value |
|---|
| Email Subject | Your alert subject |
| Alert Image | ={{$json.gif_base64}} |
| Alert Title | Your alert title |
| Site Name | ={{$json.track_state.site_name}} |
| Event Timestamp | ={{$json.createdEvent.startTime}} |
| Camera Name | ={{$json.track_state.datasource_name}} |
| Event ID | ={{$json.createdEvent.id}} |
| To Recipients | Your alert distribution list |
Step 5: Close Event path
When the orchestrator routes to “Close Event” (the track moved away or expired):
Node: Event Manager → Close Event
| Parameter | Value |
|---|
| Event ID | ={{$json.eventOrchestrator.global_event_id}} |
| End Time | ={{$json.track_state.last_seen}} |
| Key | Value |
|---|
| duration | ={{Math.round((new Date($json.track_state.last_seen) - new Date($json.eventOrchestrator.event_start_time)) / 1000)}} |
How it works end-to-end
- An object enters a monitored zone
- The trigger starts receiving
track_updated signals
- The Type I check evaluates: intersection, dwell time, velocity — fails (thresholds not yet met)
- The orchestrator routes to “No Action”
- Once thresholds are met (e.g., dwell time exceeds 300s) — passes
- The orchestrator routes to “Create Event” — image captured, event created, GIF generated, email sent
- Object continues in zone — orchestrator routes to “Update Event” (unwired, no action)
- Object leaves or track expires — checks fail → orchestrator routes to “Close Event” with duration
Other use cases for this pattern
The streaming track state pattern works for any use case where you need real-time alerting on individual track behavior:
| Use Case | Check Differences | Key Difference |
|---|
| Loitering | Type I: higher dwell time threshold | Same as zone intrusion but with stricter dwell requirements. |
| Speeding in zone | Type I: velocity > threshold, no dwell time | Inverted velocity check — fires when objects move too fast. |
| Dwell time monitoring | Type I: dwell time only, no velocity | Simpler threshold configuration. |
| Extended vehicle stop | Type I: high dwell + low velocity | Similar to obstruction but with real-time alerting. |
Testing with Replay
- Disable the Detection Webhook Trigger
- Enable the Replay Detection Trigger
- Enter a track ID from a known event
- Run the workflow — it replays the historical detections through the same logic
- Verify the event was created and closed correctly
- The replay trigger can auto-clean events created during testing
