Bearing Distance Resection Calculator

The Bearing Distance Resection Calculator finds your own position from bearing and/or distance readings to two known points — the classic surveying technique called resection. Standing somewhere unknown, you sight two landmarks whose coordinates you already know, note the compass bearing and/or distance to each, and this calculator solves for the coordinates you're standing at.

This is the mirror image of a tool like Geo Distance Calculator or Bearing Calculator: those start from two known points and find the bearing/distance between them. Resection starts from two known points and an observation from an unknown third point, and solves for that third point.

How to use it

1. Enter the latitude/longitude of Point A and Point B — two landmarks or survey control points whose coordinates you already know. Coordinates accept decimal degrees or DMS (40°42'46"N).
2. For each point, enter either the bearing you observed from your position to it, or the distance you measured to it — never both, and never neither. Bearing is a compass heading in degrees (0-360, north = 0). Distance is in meters.
3. If your inputs include a distance (to either point), pick which side of the line from A to B your position is on — distance observations always produce two mirror-image candidate positions, and this tells the calculator which one you actually are.
4. Read the resected coordinates, plus a verification bearing and distance back to both A and B — check these against your original field readings to sanity-check the fix.

The three resection methods

Which method runs is decided automatically by which fields you filled in:

• Bearing + Bearing (both points give a bearing): your position is the intersection of the two back-bearing lines — one straight line from each known point, in the reverse of the observed direction. This has a single solution (as long as the two bearings aren't parallel), so the "side" field doesn't apply.
• Distance + Distance (both points give a distance): this is trilateration — your position is one of the two points where a circle of the given radius around A intersects a circle of the given radius around B. The "side" field picks which of the two.
• Bearing + Distance (one point gives a bearing, the other a distance): your position lies on the bearing line from the first point, at the range from the second point that also satisfies the observed distance — a line/circle intersection, which again can have two solutions.

Internally, coordinates are projected onto a local flat plane centered between the two known points (the standard "plane surveying" approximation used for site-scale work), the resection is solved as ordinary 2D line/circle geometry, and the result is projected back to latitude/longitude. This matches how resection is done in practice and is accurate at the scale it's normally used for — a single site or survey area, not intercontinental distances.

Worked example

Point A at 40.7484, -73.9857 and Point B at 40.7527, -73.9772, with a bearing of 249.71° to A and 38.22° to B, resects to approximately 40.7500, -73.9800 — with a verification distance of about 512 m to A and 382 m to B.

Frequently asked questions

Why do I need to pick a "side"?

A single distance measurement puts you anywhere on a circle; two distance measurements narrow that down to (generically) exactly two points, which are mirror images of each other across the line joining the two known points. There's no way to tell them apart from the distance alone — you have to say which side of that line you're actually on. The same ambiguity can show up in the mixed bearing+distance method too, if the bearing ray happens to cross the distance circle twice; only the pure bearing+bearing method is always a single, unambiguous fix.

What if my bearings can't produce a fix?

If both bearings point in exactly the same (or exactly opposite) direction, the two back-bearing lines are parallel and never meet — there's no unique position. Take one more careful reading; even a degree or two of separation is enough for a strong fix.

Can I mix a bearing to one point with a distance to the other?

Yes — that's the third supported method, common when a total station or laser rangefinder gives you a precise distance to one landmark but only a compass bearing to the other.

Is my data sent anywhere?

No. All calculations run locally in your browser. Your coordinates never leave your device.