You can see a landmark from two places, but you do not know where it is on the map. Take a compass bearing from each place, enter the two known points and the two bearings here, and this tool works out where the bearing lines cross. It is free, works in your browser, and is a handy check for hikers, sailors and orienteers.
What triangulation is
Triangulation is one of the oldest navigation methods. If you know where you are and you measure the direction to a target, you know the target lies somewhere along that direction line, but not how far away. Measure the direction again from a second known point, and the target must lie on that line too. The only point on both lines is where they cross, and that crossing is the target’s position. Sailors call this a fix, and it works with a compass, a map and two viewpoints. This tool does the geometry for you, so you can focus on taking good bearings instead of doing trigonometry on a hillside.
How the tool computes the fix
The tool converts your two known points into a flat local map centred on the first point, using the standard approximation that one degree of latitude is about 111 kilometres and one degree of longitude is 111 kilometres times the cosine of the latitude. Each bearing becomes a direction vector: a bearing of 0 degrees points north, 90 degrees points east, and so on clockwise. The tool then solves for the point where the two direction lines meet. From that point it converts back to latitude and longitude, measures the distance from each known point, and computes the crossing angle between the two lines. A crossing near 90 degrees gives a strong fix, while a narrow crossing gives a weak one, because a small bearing error then moves the fix a long way.
How to use the planner
Stand at your first known point and note its latitude and longitude from a map or a GPS reading. Point your compass at the target and read the bearing in degrees clockwise from north. Walk to a second known point, ideally some distance away and not in line with the target, and repeat. Enter both points and both bearings, then press the button. The tool shows the target’s latitude and longitude, the distance from each point, and the crossing angle with a quality note. Plot the result on your map and check it against what you can see: the fix should agree with the landscape.
Getting good bearings
Good bearings matter more than good math. Hold the compass level and away from metal objects, phones and magnets, which can pull the needle off. Sight carefully along the compass direction finder, not roughly over the top of the case. Take each bearing twice and use the average if they differ. Remember the difference between magnetic north and true north: most compasses point to magnetic north, while maps use true north, and the gap between them, called declination, can be several degrees. If your map gives a declination figure, correct your bearings before entering them, or your fix will be shifted. Finally, choose viewpoints with a wide gap between them: two points close together give a narrow crossing and a poor fix.
When triangulation is most useful
Triangulation shines when you can see a target but cannot reach it, such as a peak across a valley, a lighthouse from a boat, or a smoke column in a forest. It is also a good cross-check for a GPS reading, because it uses completely different information. Rescue teams use it to locate signals, and surveyors use refined versions of it to map land. For walkers, it is a satisfying way to confirm a position on a paper map without batteries. The tool’s distance figures also help you judge whether a target is a realistic walk or a distant landmark to admire from where you stand.
Limits and safety notes
The tool uses a flat-earth approximation over short distances, so it is accurate for fixes within a few tens of kilometres, but not for continental distances. It assumes your bearings are correct and your known points are exact: a one-degree bearing error over 10 kilometres moves the fix by about 175 metres. Never rely on a single fix for safety-critical decisions. Use it alongside a map, a GPS device, and your own judgement, and always let someone know your plans when you head into wild country.
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Versión en español: Planificador de Triangulación con Brújula – Encuentra Posición con Dos Rumbos