Red Grid Link

Offline MGRS navigation and proximity team coordination for small teams (2-8 people). No cell service needed.

Built on the MGRS engine from Red Grid MGRS. Field Link adds zero-config proximity sync over Bluetooth, with Apple Multipeer Connectivity (iOS) and Google Play Services Nearby Connections (Android) running alongside as a parallel higher-bandwidth transport -- your team appears on the map the moment they're in range.

Solo navigator? Red Grid MGRS gives you the same MGRS engine as a standalone tool with DAGR-class precision, 9 tactical tools, and 6 radio-ready report templates. Part of the Red Grid Tactical ecosystem.

Available now on iOS. Android version in closed beta testing.

Screenshots

Features

MGRS-Native Navigation

Live Military Grid Reference System coordinates with 1-meter precision. GPS Kalman filter for smooth, accurate position tracking. MGRS grid overlay on offline maps from GZD down to 100m resolution. Bearing, distance, dead reckoning, resection, pace count (with accelerometer step detection), declination, and coordinate conversion tools. NATO phonetic voice readout for hands-free grid calls.

Field Link -- Team Sync Without Infrastructure

Zero-config proximity sync over BLE on all platforms, with Apple Multipeer Connectivity (AWDL) added on iOS for higher-bandwidth peer transport when the app is backgrounded. Devices within range automatically discover each other and share position, marker, and annotation data. No internet required. No pairing codes. No servers. (Android Wi-Fi Direct / Nearby Connections is on the roadmap; the shipping Android build is BLE-only.)

• 2-8 devices per session
• AES-256-GCM encryption with ECDH P-256 ephemeral keys for PIN and QR sessions; Open sessions are unencrypted by design (training / demo use)
• Tiered session security: Open (auto-join, no encryption), PIN (4-digit, encrypted), QR code (host-generated session secret, encrypted)
• Delta payloads under 200 bytes per position update
• Ghost markers with time-decay visualization when teammates disconnect
• Velocity vectors project last-known movement direction
• Expedition Mode: <3% battery/hr (BLE-only, 30s updates)
• Ultra Expedition Mode: <2% battery/hr (BLE-only, 60s updates)
• Auto-reconnect with exponential backoff on disconnect

Offline Maps

Download map packs from OpenStreetMap or OpenTopoMap to MBTiles for offline operation, with MGRS grid lines rendered as a dynamic overlay. Region downloads are throttled to respect public-tile-server usage policies; for sustained heavy offline usage we recommend a licensed provider. (Native USGS / Mapbox / MapTiler integrations are on the roadmap.)

4 Operational Modes

One engine, four presentation layers. Terminology, icons, and quick actions adapt to your mission:

• Search & Rescue -- sector assignments, clue markers, search patterns
• Backcountry -- camp, waypoint, and trail navigation
• Hunting -- stand locations, game sightings, property boundaries
• Training -- exercise objectives, rally points, phase lines

11 Tactical Tools

Dead Reckoning, Resection, Pace Count, Bearing/Back Azimuth, Coordinate Converter (MGRS/Lat-Lon/DMS/UTM), Range Estimation, Slope Calculator, ETA/Speed Calculator, Magnetic Declination, Celestial Navigation, MGRS Precision Reference.

Team Coordination (V1.3)

Assign roles (Lead, Scout, Medic, Comms, custom) with callsigns. Lead controls the session like a group admin. Share waypoints with the whole team or save them privately. Draw tap-to-place annotations visible to all peers. Set boundary geofences with automatic alerts when someone crosses. NATO phonetic voice callouts announce teammate positions hands-free. Export and import sessions as versioned JSON for backup and review.

Extended Range + Navigation (V1.4)

BLE Long Range (Coded PHY) extends range from ~100m to 400m-1km on supported devices. Live RSSI signal bars show connection quality for each teammate with warnings when signal weakens. FixPhrase encodes any location as 4 easy-to-remember words (~11m accuracy, order-independent). Choose between OpenStreetMap or OpenTopoMap when downloading offline regions. Coordinate bar cycles between MGRS and FixPhrase display.

Security + Communication (V1.5)

Real ECDH P-256 key exchange with per-peer derived encryption keys. Actual BLE Coded PHY negotiation for extended range on Android. One-tap emergency beacon sends GPS coordinates to all team members with 30-second retransmission. 7 pre-canned tactical messages (HELP, STOP, RALLY ON ME, ALL CLEAR, FOUND SOMETHING, HEADING BACK, NEED SUPPLIES) plus 160-character free text over encrypted CRDT sync.

After-Action Reports

One-tap PDF export: map snapshot, mission timeline, track data, timestamps, team roster with roles, per-member tracks, boundary events, markers, and session log. Share via AirDrop, file share, or any local transfer.

4 Tactical Themes

Red Light (night vision, free), NVG Green (Pro), Day White (Pro), Blue Force (Pro).

How It Works

Solo Mode

Open Red Grid Link and your MGRS position appears on the offline map. Navigate using bearing, distance, and dead reckoning tools -- identical to Red Grid MGRS but with a full map view and 11 tactical tools.

Field Link (Team Mode)

1. Start a session -- tap one button to begin broadcasting over BLE
2. Set security -- choose Open, PIN, or QR code authentication
3. Teammates appear -- any device running Red Grid Link within range (~100-300m standard, up to 1km with BLE Long Range) is automatically discovered
4. Positions sync -- delta updates flow between all devices at configurable intervals; PIN and QR sessions wrap each delta in an AES-256-GCM envelope, Open sessions send plaintext
5. Ghosting -- if a teammate moves out of range, their last-known position remains on your map with time-decay opacity (100% to outline over 30 minutes)
6. Reconnect -- when a ghost comes back in range, their marker snaps to live position

No accounts. No servers. No cell service. No configuration. It just works.

Free vs Pro

Pricing:

• Free -- All modes, 2-device Field Link, 1 map region, Red Light theme
• Pro -- $3.99/mo or $29.99/yr
• Pro+Link -- $5.99/mo or $44.99/yr (Pro + full 8-device Field Link)
• Team -- $199.99/yr (8 seats, includes Pro+Link for all members)
• Lifetime -- $149.99 one-time (Pro+Link forever)

Privacy

No accounts. No analytics. No ad networks. No third-party data SDKs. Privacy-safe crash reporting (Sentry, release mode only — no location data transmitted). In-app purchases processed by Apple/Google -- Red Grid Link never sees your payment details. Full details in PRIVACY.md.

Build from Source

git clone https://github.com/RedGridTactical/RedGridLink.git
cd RedGridLink
flutter pub get
flutter pub run build_runner build --delete-conflicting-outputs
flutter run

Requires Flutter SDK. Currently targeting iOS -- Android support is planned. All free features work from source. Pro features require a valid purchase through Apple. Field Link requires Bluetooth and location permissions on physical devices.

Roadmap

Full roadmap with feature checklists: ROADMAP.md

Ongoing

• Security audits and cryptographic library updates
• Battery performance optimization
• Map tile source expansion
• Test coverage expansion (target 90%+)
• Store listing optimization and A/B testing

Contributing

Red Grid Link is built in the open. We welcome bug reports, feature requests, and pull requests.

• Report a bug: Open an issue
• Request a feature: Start a discussion
• Submit a PR: Fork, branch, and open a pull request

See the Roadmap for planned features and where help is needed.

Red Grid Tactical Ecosystem

Website: redgridtactical.com

License

MIT + Commons Clause -- free for personal non-commercial use. Commercial and organizational deployment requires written permission.

Contact: [email protected]

Your team. Your grid. No cell towers required.

If Red Grid Link helps you stay coordinated in the field, give it a star and share it with your team.