Compass Triangulation

User Manual

Find a position on the map from nothing but compass bearings.

Mobile Screenshots

The Problem It Solves

You can see something — smoke on a ridgeline, a distress flare, a downed aircraft, an animal, a suspicious vehicle — but you can't reach it, and "somewhere over that way" isn't a location anyone can act on.

If you and a teammate (or you, moving between two spots) can each take a compass bearing toward the same thing, the point where those bearings cross is its location.

This is classical resection, the same technique search-and-rescue teams, surveyors, and foresters have used for decades — Compass Triangulation just does the trigonometry, the mapping, and the reporting for you, in the field, on your phone.

Getting Started

1. Set Your Magnetic Declination

Your compass points to magnetic north; maps and GPS coordinates use true north. The gap between them — declination — varies by location and drifts over time, and it has to be corrected for or your bearings will be off. Enter it manually under Settings, or, with Pro, let the app fetch the current value automatically from your GPS position.

2. Understand the Two Numbers Per Bearing

Every bearing you add shows both the raw compass heading (magnetic) and the true-north-corrected heading — the app does this conversion for you so you never have to do it by hand under pressure.

Adding Bearings

You have three ways to add a bearing, and you can mix all three in the same session:

Live capture. With GPS on, point your phone in the direction of the object and tap to record your current location and the device compass's heading in one action.
Manual entry. Type in an origin location and a heading directly — useful for entering a bearing someone radioed in to you.
Import via QR or link. If a teammate shares a bearing from their device, scan their QR code or open their link to add it to your session instantly.

Add at least two bearings from different locations, aimed at the same object, for the app to compute anything. More bearings, and bearings taken from more different angles to each other, produce a tighter, more reliable result — two bearings that cross at a shallow angle leave more room for error than two that cross close to perpendicular.

Reading the Result

Once you have two or more non-parallel bearings, the app automatically shows:

The intersection point — the computed real-world location, as latitude/longitude, UTM, and MGRS
Triangulation Confidence (Good / Fair / Poor) — based on how sharply your bearings cross; the app tells you outright when your geometry is shaky, rather than just handing you a number
Estimated Uncertainty — a radius, shown as a dashed circle on the map, representing how much real-world error to expect around the computed point
Nearest address, when available

The map shows every bearing as a line from its origin, your computed intersection as a marker, and the uncertainty circle around it.

Sharing and Exporting

QR code or link, from the Share screen — this includes your declination setting, so whoever opens it gets the same real-world point regardless of what declination their device has set.
JSON export/import — your full bearing set, for backup or moving to another device.
GPX export (Pro) — for loading directly into Garmin devices, Gaia GPS, CalTopo, QGIS, or whatever mapping tool your team already uses.

Pro Features in Practice (only available in IOS App)

Saved Sessions — Tap Save Session, give it a name, and come back to it later without re-entering every bearing. Useful the moment you're juggling more than one active search or survey.

PDF Field Report — Tap the report button to generate a complete, shareable document: the map with every bearing and the computed intersection drawn on it, a table of every bearing with both heading types, coordinates in three formats, your confidence rating and uncertainty radius, and the nearest address — plus two QR codes (one to get the app, one carrying your actual bearing data) so anyone you hand it to can pull it up themselves.

CAP Search Grid — Toggle this on to overlay standard Civil Air Patrol search-grid lines on the map, if your team coordinates using that reference system.

Offline Maps — Before you lose signal, draw a rectangle over the area you're about to operate in, choose how much extra zoom detail you want, and download it. The app shows a size estimate before you commit, and a running total of what's actually stored on your device afterward — this isn't a passive cache, it's a deliberate "I'm going here" action you take in advance.

Keep Screen Awake — Locks your screen on while you're actively working, so a timeout doesn't interrupt you mid-triangulation.

A Quick Worked Example

From your position, you see smoke on a distant hillside. Point your phone at it and capture a live bearing.
Drive or hike half a mile to a different vantage point where you can still see the smoke. Capture a second live bearing.
The app immediately shows an intersection point, a confidence rating, and an uncertainty radius.
If the confidence is "Poor," your two vantage points were too close to the same angle — move further around and take a third bearing from a more different direction.
Generate a PDF Field Report and share it with your incident commander, or export GPX and load it straight into the team's GPS units.

Tablet Screenshots

By accessing this application you hereby agree to the terms of our Software Disclaimer and of our Privacy Policy.

Open Source Acknowledgments

This app uses the following open-source libraries:

html5-qrcode — mebjas (Minhaz Av). Apache License 2.0. https://github.com/mebjas/html5-qrcode

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