Polaroid
Provides a FastAPI REST server with endpoints for node/edge management, merging, and context retrieval, compatible with OpenAI's function-calling format for use with agents like Codex CLI.
polaroid
Embeddable CRDT scene graph for embodied AI agents.

Quick Start · How It Works · CLI Reference · GitHub Action · vs. Alternatives · Contributing
Why
Multiple robots navigating the same building each build their own private map. When robot A opens a door and robot B hasn't been told, they diverge. Sharing a map requires a central server — which is a single point of failure.
polaroid solves this with a CRDT scene graph: a persistent, mergeable map of nodes (objects, rooms, surfaces) and edges (spatial relationships). Two robots can merge their maps without a server, without conflicts, without data loss. CRDT semantics guarantee the merge is always safe, deterministic, and idempotent.
# Share your scene graph with a peer
polaroid merge /path/to/peer/scene.dbRelated MCP server: state-trace
How It Works
flowchart LR
A[Agent observes\nroom / object / surface] --> B[SceneNode added\nto SceneStore]
A --> C[SceneEdge added\ncontains / adjacent-to]
B & C --> D{Peer agent\nhas different view}
D --> E[SceneMerger.merge\nCRDT semantics]
E --> F[Grow-only nodes\nconfidence-weighted LWW]
F --> G[Unified scene graph\nno server required]Core primitives:
SceneNode — a content-addressed node (object, room, surface, region, or agent). ID = SHA-256[:16] of
label|node_type. Same label and type always produce the same ID regardless of agent.SceneEdge — a directed spatial relationship between two nodes (
contains,adjacent-to,on-top-of,blocks,connects). ID = SHA-256[:16] ofsource_id|target_id|relation.SceneStore — SQLite-backed persistent store. Zero dependencies beyond Python stdlib + click/rich.
SceneMerger — CRDT merge: nodes are grow-only (never deleted), conflicting property updates resolved by confidence-weighted last-write-wins.
SceneQuery — query by type, label substring, confidence, or spatial neighbors.
Features
Feature | Details |
Content-addressed nodes | Same label+type always produces the same ID — no duplicates |
CRDT merge semantics | Grow-only sets + confidence-weighted LWW registers |
Conflict-free merge |
|
Spatial queries | Find nodes by type, label, or neighbors via edge traversal |
Context summary | One-call text description of the scene for LLM prompts |
Offline / local-first | Single SQLite file, no server required |
FastAPI REST server |
|
MCP server | Model Context Protocol integration for Claude and other agents |
202 tests | Comprehensive test suite covering all layers |
Quick Start
pip install polaroid-aifrom polaroid import SceneNode, SceneEdge, SceneMerger, SceneQuery, SceneStore
# Robot A observes a kitchen
store_a = SceneStore("/tmp/robot-a.db")
kitchen = SceneNode(label="room-kitchen", node_type="room", properties={"floor": "tile"})
table = SceneNode(label="table-A", node_type="object", properties={"color": "brown"}, confidence=0.9)
store_a.upsert_node(kitchen)
store_a.upsert_node(table)
edge = SceneEdge(source_id=kitchen.id, target_id=table.id, relation="contains")
store_a.upsert_edge(edge)
# Robot B observes the same room with a door
store_b = SceneStore("/tmp/robot-b.db")
store_b.upsert_node(kitchen) # same ID — no duplicate
door = SceneNode(label="door-1", node_type="object", properties={"state": "open"})
store_b.upsert_node(door)
# Merge B into A — CRDT guarantees safety
result = SceneMerger().merge(store_a, store_b)
print(result.summary())
# Added 1 nodes, updated 0 nodes, added 0 edges, resolved 0 conflict(s).
# Query the unified scene
q = SceneQuery(store_a)
print(q.context_summary())
# 1 rooms, 2 objects. Known objects: table-A, door-1. 1 spatial relationship recorded.
store_a.close()
store_b.close()CLI Reference
polaroid [--db PATH] COMMAND [OPTIONS]Command | Description | Key options |
| Add a node to the scene |
|
| Add a directed edge |
|
| Query nodes |
|
| Merge another scene store into this one | — |
| Show node/edge counts and context | — |
Global options:
Option | Default | Env var |
|
|
|
Examples:
# Add nodes
polaroid add-node door-1 object --confidence 0.95 --property state=open --property color=brown
polaroid add-node room-kitchen room
# Add an edge
polaroid add-edge <door-id> <kitchen-id> contains
# Query the scene
polaroid query --type object
polaroid query --label door --min-confidence 0.8 --format json
# Merge peer's scene
polaroid merge /path/to/peer.db
# Status overview
polaroid statusGitHub Action
Add polaroid scene merge to your CI pipeline:
# .github/workflows/polaroid.yml
name: polaroid scene check
on: [push, pull_request]
jobs:
scene:
runs-on: ubuntu-latest
steps:
- uses: actions/checkout@v4
- uses: sandeep-alluru/polaroid@main
with:
db: .polaroid/scene.db
fail-on-empty: "false"The action installs polaroid and runs polaroid status. See docs/github-action.md for full documentation.
vs. Alternatives
polaroid | ROS 2 map server | Semantic Fusion | Hydra (Facebook) | LangGraph checkpointing | |
CRDT merge | Yes — grow-only + confidence LWW | No | No | No | No |
Serverless | Yes — single SQLite file | Requires ROS master | Requires GPU | Requires server | Partial |
Content-addressed IDs | Yes — SHA-256[:16] | No | No | No | No |
MCP / LLM integration | Yes — MCP server | No | No | No | No |
Offline / embedded | Yes | Partial | No | No | Partial |
Primary purpose | CRDT scene graph for multi-agent | ROS navigation maps | Dense 3D fusion | Neural scene representation | LLM state persistence |
Open source | MIT | Apache 2.0 | Research | BSD | Apache 2.0 |
polaroid is not a 3D reconstruction system. It is designed for: "Given that multiple agents observed different parts of the world, how do we merge their maps safely?"
Claude / MCP integration
polaroid ships a Model Context Protocol server that lets Claude and other MCP-compatible agents record and query scene nodes directly:
# Start the MCP server
python -m polaroid.mcp_server
# In your Claude Code project's .claude/settings.json:
{
"mcpServers": {
"polaroid": {
"command": "python",
"args": ["-m", "polaroid.mcp_server"]
}
}
}Once connected, Claude can call add_scene_node, query_nodes, and get_context as tools. See docs/mcp.md for the full tool schema.
OpenAI integration
polaroid exposes a FastAPI REST server compatible with OpenAI's function-calling format. The tool definitions are in tools/openai-tools.json and the full API spec is in openapi.yaml.
# Start the REST server
uvicorn polaroid.api:app --reload
# Pass to Codex CLI or any OpenAI-compatible agent
codex --tools tools/openai-tools.json "Show me all objects in the scene"Endpoints: GET /health, POST /node, POST /edge, GET /nodes, POST /merge, GET /context. See docs/openai.md for details.
Case Studies
See how teams are using polaroid in production:
Repository structure
polaroid/
├── src/
│ └── polaroid/
│ ├── graph.py # SceneNode, SceneEdge, MergeResult dataclasses
│ ├── store.py # SQLite-backed SceneStore
│ ├── merger.py # SceneMerger CRDT merge algorithm
│ ├── query.py # SceneQuery — find_nodes, find_neighbors, context_summary
│ ├── export.py # to_dot(), to_json(), to_adjacency_matrix() exporters
│ ├── stats.py # GraphStats, compute_stats(), cluster_by_type(), most_connected()
│ ├── subgraph.py # extract_subgraph(), filter_by_type(), neighborhood()
│ ├── report.py # print_scene(), print_merge(), to_json(), to_markdown()
│ ├── cli.py # Click CLI (add-node, add-edge, query, merge, status, stats, export)
│ ├── api.py # FastAPI REST server
│ └── mcp_server.py # MCP server
├── tests/
│ ├── test_graph.py # SceneNode, SceneEdge, MergeResult unit tests
│ ├── test_store.py # SceneStore upsert/get/list tests
│ ├── test_merger.py # SceneMerger CRDT merge tests
│ ├── test_query.py # SceneQuery tests
│ ├── test_export.py # Export formatter tests
│ ├── test_stats.py # Graph analytics tests
│ ├── test_subgraph.py # Subgraph extraction tests
│ ├── test_report.py # Report formatter tests
│ ├── test_cli_runner.py # Click CliRunner tests
│ └── test_api.py # FastAPI TestClient tests
├── examples/
│ └── demo.py # Standalone demo script
├── docs/ # MkDocs documentation
├── tools/
│ └── openai-tools.json # OpenAI function-calling tool definitions
├── assets/
│ ├── hero.png # README hero image
│ └── logo.png # Project logo
├── action.yml # GitHub Action
├── openapi.yaml # OpenAPI 3.1 spec
├── pyproject.toml # Package metadata + dependencies
└── CONTRIBUTING.md # Contribution guideAdvanced API
These functions are exported at the top level (from polaroid import ...) and cover graph analytics, DOT export, and subgraph extraction.
compute_stats(store) -> GraphStats
Returns aggregate statistics about a SceneStore.
from polaroid import SceneStore, compute_stats
store = SceneStore("/tmp/scene.db")
stats = compute_stats(store)
print(stats.node_count) # total nodes
print(stats.edge_count) # total edges
print(stats.avg_confidence) # mean confidence across all nodes
print(stats.most_common_type) # node type with the highest countto_dot(store) -> str
Serialises the scene graph as a Graphviz DOT string, ready for rendering with dot -Tpng.
from polaroid import SceneStore, to_dot
store = SceneStore("/tmp/scene.db")
dot_src = to_dot(store)
print(dot_src)
# digraph polaroid {
# "abc123" [label="kitchen (room)"];
# "def456" [label="table-A (object)"];
# "abc123" -> "def456" [label="contains"];
# }
with open("scene.dot", "w") as f:
f.write(dot_src)
# Then: dot -Tpng scene.dot -o scene.pngextract_subgraph(store, node_ids) -> SceneStore (in-memory)
Returns a new in-memory SceneStore containing only the specified nodes and the edges that connect them.
from polaroid import SceneStore, SceneNode, extract_subgraph
store = SceneStore("/tmp/scene.db")
# Get IDs of interest from a query, then extract
kitchen = SceneNode(label="room-kitchen", node_type="room")
table = SceneNode(label="table-A", node_type="object")
sub = extract_subgraph(store, [kitchen.id, table.id])
print(sub.list_nodes()) # only kitchen + tableneighborhood(store, node_id, radius=1) -> list[SceneNode]
Returns all nodes reachable from node_id within radius hops (BFS over edges). Useful for building local context windows for LLM prompts.
from polaroid import SceneStore, SceneNode, neighborhood
store = SceneStore("/tmp/scene.db")
kitchen = SceneNode(label="room-kitchen", node_type="room")
nearby = neighborhood(store, kitchen.id, radius=2)
for node in nearby:
print(node.label, node.node_type)GitHub Topics
Suggested topics for discoverability:
ai-agents crdt scene-graph spatial-memory robotics embodied-ai sqlite mcp openai llm-tools multi-agent python
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