Composing Checks

The composable approach

Worlds provides check nodes that can be combined to express any detection use case. Which check nodes are available depends on the signal type from your trigger:

Signal Type	Check Nodes	Question
Track State	Type I, Type II, Type III	What is this specific track doing?
Zone State	Zone Activity Check	What is happening in this zone?

Rather than building specialized nodes for each use case, you compose these check types — and optionally add external checks like VLM — to express your business logic.

Track state compositions

Each track check type writes its results to a separate namespace — checks.type1, checks.type2, checks.type3 — and preserves all input data. This means you can chain them in sequence:

Trigger → Type I Check → Type II Check → Event Orchestrator

The Event Orchestrator reads the combined checks object and evaluates all results using AND or OR logic to decide whether to create, update, or close an event.

Type I alone — track in zone

The simplest and most common pattern. A single Type I check handles use cases like:

Obstruction/loitering (dwell + velocity thresholds)
Zone intrusion (intersection threshold)
Speeding in zone (velocity threshold)

Trigger → Type I → Event Orchestrator → Event Manager

Type I + Type II — zone sequence with thresholds

Combine zone presence conditions with directional/sequence validation:

Wrong-way detection with speed check (was the vehicle going fast in the wrong direction?)
Checkpoint compliance (did the vehicle stop at checkpoint A before entering zone B?)

Trigger → Type I → Type II → Event Orchestrator → Event Manager

Type I + Type III — proximity in zone

Combine zone-based conditions with track-to-track interaction:

Person near forklift in a specific zone
Two vehicles overlapping in a loading bay

Trigger (batch) → Type I → Type III → Event Orchestrator → Event Manager

Type III requires batch mode because interaction data is only available after tracks expire.

All three types

For complex safety rules:

Person entered restricted zone (Type I), bypassed the checkpoint (Type II), and was near equipment (Type III)

Trigger (batch) → Type I → Type II → Type III → Event Orchestrator → Event Manager

Zone state checks

For zone state workflows, the Zone Activity Check evaluates zone-level conditions. It writes results to checks.zoneActivity:

Trigger (zone state) → Zone Activity Check → Event Orchestrator → Event Manager

This is used for congestion, congregation, and occupancy monitoring where you care about the aggregate number of tracks in a zone rather than any specific track.

Adding VLM (Vision Language Model) checks

For workflows that capture images, you can add a VLM check as an additional confirmation layer. This uses the built-in LLM nodes rather than a Worlds custom node:

Trigger → Check → Orchestrator → Capture Image → VLM Chain → IF (boolean) → Event Manager

The VLM analyzes the captured image and returns structured output (e.g., { "confirmed": true, "confidence": 0.92, "context": "..." }). You can use this two ways:

As a check gate — feed the VLM boolean into an IF node to conditionally create events. This adds AI confirmation to reduce false positives.
As context metadata — always create the event but attach the VLM description and confidence as event metadata for human review.

See the Streaming Zone State Workflow for a complete VLM integration example.

Output accumulation

As data flows through multiple check nodes, the checks object accumulates:

{
  "track_state": { ... },
  "checks": {
    "type1": {
      "passed": true,
      "matching_zones": ["79"],
      "zone_details": { ... }
    },
    "type2": {
      "passed": true,
      "matching_zones": ["zone_b"],
      "track_sequence": ["zone_a", "zone_c", "zone_b"],
      "sequences": [ ... ]
    }
  }
}

The Event Orchestrator evaluates all checks entries:

AND mode — all checks must pass for conditions to be met
OR mode — any check passing is sufficient

Logic within vs. across checks

Understanding the logic layers:

Level	Logic	Description
Within a zone	AND	All enabled thresholds must pass for a zone to match
Across zones	OR	At least one zone must match for the check to pass
Across check types	AND or OR	Configured on the Event Orchestrator

Start with a single check type for most use cases. Add Type II or Type III only when your use case genuinely requires sequence or interaction detection. Simpler workflows are easier to debug and maintain.

Common compositions reference

Use Case	Signal Type	Mode	Checks	Description
Obstruction / loitering	Track State	Batch or Streaming	Type I	Dwell time + low velocity in zone
Wrong-way detection	Track State	Streaming	Type II	Zone sequence in forbidden order
Safety near-miss	Track State	Batch	Type III	Person/vehicle proximity
PPE compliance	Track State	Batch	Type III	Person/PPE bbox overlap
Congestion	Zone State	Streaming	Zone Activity	Track count threshold in zone
Congregation	Zone State	Streaming	Zone Activity	People gathering in area
Speeding in zone	Track State	Streaming	Type I	High velocity in zone
Unauthorized entry	Track State	Streaming	Type I + II	Zone presence + bypassed checkpoint
Person-vehicle in zone	Track State	Batch	Type I + III	Zone presence + interaction
VLM-confirmed congestion	Zone State	Streaming	Zone Activity + VLM	Zone check + image confirmation

Getting Started

Concepts

Workflow Guides

Advanced

The composable approach

Track state compositions

Type I alone — track in zone

Type I + Type II — zone sequence with thresholds

Type I + Type III — proximity in zone

All three types

Zone state checks

Adding VLM (Vision Language Model) checks

Output accumulation

Logic within vs. across checks

Common compositions reference

​The composable approach

​Track state compositions

​Type I alone — track in zone

​Type I + Type II — zone sequence with thresholds

​Type I + Type III — proximity in zone

​All three types

​Zone state checks

​Adding VLM (Vision Language Model) checks

​Output accumulation

​Logic within vs. across checks

​Common compositions reference

The composable approach

Track state compositions

Type I alone — track in zone

Type I + Type II — zone sequence with thresholds

Type I + Type III — proximity in zone

All three types

Zone state checks

Adding VLM (Vision Language Model) checks

Output accumulation

Logic within vs. across checks

Common compositions reference