Spotter Relay and Triangulation Guide

Spotter Relay: Two Vectors in Sequence

Use a relay when the report describes a path: gun to spotter, then spotter to target. The first bearing and distance start at the gun. The second bearing and distance start at the spotter. Projecting those two vectors locates the target. After that, calculate the final bearing and range directly from the original gun to the target. The spotter helps locate the target but never replaces the gun as the firing origin.

Open Relay mode in the Firing Solution Planner when both legs provide a bearing and distance. Keep the measurements attached to their own leg. Entering the second bearing from the gun instead of the spotter produces a clean-looking but incorrect target coordinate.

Triangulation: Two Constraints Meet

Use triangulation when two reports independently constrain the same target. Two stations may each provide a bearing, one station may provide a bearing while another provides a distance, or two stations may each provide a distance. These are not sequential travel legs. The solution is the point or points where the rays and circles intersect.

The Triangulation Calculator supports bearing–bearing, bearing–distance, and distance–distance input. Select the matching mode before entering coordinates. Each bearing remains attached to its observer; each distance creates a circle around its own station.

How to Choose the Correct Method

1. Ask whether the first report locates a second observer or already constrains the target.
2. If the second measurement begins at the point found by the first, use a relay.
3. If both reports independently describe the target, use triangulation.
4. If there is only one gun-to-target bearing and range, use Direct mode instead.
5. If a report lacks an origin, do not guess; return to the map or order and identify it.

A useful shorthand is “relay follows; triangulation intersects.” The shorthand does not replace reading the origins, but it prevents many mode-selection errors.

Relay Workflow

First record the gun coordinate. Enter the gun-to-spotter bearing and distance to locate the spotter. Compare that computed spotter position with any known map reference. Next enter the spotter-to-target bearing and distance. Inspect the resulting target on the north-up plot. Finally read the gun-to-target bearing and range returned by the planner. Carry that final range—not either relay-leg distance—to the Ballistic Calculator.

If the final target appears on the wrong side of the observer, check whether a bearing was reversed by 180 degrees or interpreted counterclockwise. If the target looks plausible but final range is surprising, verify that the gun origin was not overwritten with the spotter coordinate.

Triangulation Workflow

Choose the constraint pair, enter station A and station B, then enter each station's own bearing or distance. Keep all distances in one unit. Solve and inspect every candidate. Bearing–bearing usually has one forward-ray intersection unless the rays are parallel or meet behind a station. A bearing and circle can meet at zero, one, or two forward points. Two circles can also return zero, one, or two points.

Two candidates are not a calculator failure. They are a real geometric ambiguity. Compare both coordinates with map boundaries, the described sector, and any additional information already present in the game. Do not select the first card simply because it is displayed first.

Worked Example: Why Origins Matter

Imagine station A at (0, 0) reports a target bearing of 45 degrees, while station B at (10, 0) reports 315 degrees. In this invented geometry example, both bearings point northward toward one intersection. If the second bearing were mistakenly entered from station A, the rays would no longer describe the same target. The numbers have not changed; only the origin assignment has, and that is enough to invalidate the solution.

For a relay example, imagine the spotter is 4 units east of the gun and the target is 3 units north of the spotter. The target is not merely 3 units from the gun. The planner must combine both legs and then measure the diagonal from the gun.

Common Mistakes and Recovery

• Treating two independent observer bearings as a two-leg relay.
• Starting both constraints at the same station.
• Using a full infinite line when the report provides a forward bearing ray.
• Mixing map units between two distance circles.
• Discarding the second valid candidate without map context.
• Carrying a relay-leg range into the firing card instead of final gun-to-target range.

When no intersection is returned, recheck station coordinates, forward direction, units, and copied decimals. Parallel bearings and non-overlapping circles can legitimately produce no solution. Do not “fix” that result by changing values until they intersect.

Completion Checklist

Before leaving the geometry stage, confirm the chosen method, both origins, bearing convention, distance unit, candidate count, selected target coordinate, final gun-to-target bearing, and final range. Use the Mils Converter only if the sight requires another angular convention. Then continue to Ballistics and verify the community-reference load in the current build.

For a complete start-to-finish sequence, return to the First Firing Solution Guide.