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bearing: fix final bearing returning values outside [-180, 180] #3077

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Merged
mfedderly merged 2 commits into from
Jun 26, 2026
+16 −1
Merged

bearing: fix final bearing returning values outside [-180, 180] #3077

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9bec005
bearing: fix final bearing returning values outside [-180, 180]
JSap0914 Jun 22, 2026
d93873a
Merge branch 'master' into fix/bearing-final-bearing-range
mfedderly Jun 26, 2026
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4 changes: 3 additions & 1 deletion packages/turf-bearing/index.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -65,7 +65,9 @@ function calculateFinalBearing(start: Coord, end: Coord) {
// Swap start & end
let bear = bearing(end, start);
bear = (bear + 180) % 360;
return bear;
// Normalize to [-180, 180]; the % 360 above yields [0, 360) which violates
// the documented return range when the initial reverse bearing is positive.
return bear > 180 ? bear - 360 : bear;
}

export { bearing };
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13 changes: 13 additions & 0 deletions packages/turf-bearing/test.ts
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Expand Up @@ -44,3 +44,16 @@ test("bearing", (t) => {
writeJsonFileSync(out + "results.geojson", results);
}
});
test("bearing - final bearing is in [-180, 180] range", (t) => {
// Traveling due west along the equator: start=(10,0), end=(0,0)
// The final bearing at the destination should be -90 (west), not 270.
const west_start = point([10, 0]);
const west_end = point([0, 0]);
const finalWest = bearing(west_start, west_end, { final: true });
t.ok(
finalWest >= -180 && finalWest <= 180,
"final bearing is within [-180, 180]: got " + finalWest
);
t.equal(finalWest.toFixed(2), "-90.00", "final bearing westward is -90");
t.end();
});
4 changes: 2 additions & 2 deletions packages/turf-helpers/README.md
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Expand Up @@ -15,13 +15,13 @@ depending on latitude.
See [https://www.thoughtco.com/degree-of-latitude-and-longitude-distance-4070616][1]
for an illustration of this behaviour.

Type: (`"meters"` | `"metres"` | `"millimeters"` | `"millimetres"` | `"centimeters"` | `"centimetres"` | `"kilometers"` | `"kilometres"` | `"miles"` | `"nauticalmiles"` | `"inches"` | `"yards"` | `"feet"` | `"radians"` | `"degrees"`)
Type: (`"meters"` | `"metres"` | `"m"` | `"millimeters"` | `"millimetres"` | `"mm"` | `"centimeters"` | `"centimetres"` | `"cm"` | `"kilometers"` | `"kilometres"` | `"km"` | `"miles"` | `"mi"` | `"nauticalmiles"` | `"nmi"` | `"inches"` | `"in"` | `"yards"` | `"yd"` | `"feet"` | `"ft"` | `"radians"` | `"rad"` | `"degrees"` | `"deg"`)

## AreaUnits

Area measurement units.

Type: (Exclude<[Units][2], (`"radians"` | `"degrees"`)> | `"acres"` | `"hectares"`)
Type: (Exclude<[Units][2], (`"radians"` | `"rad"` | `"degrees"` | `"deg"`)> | `"acres"` | `"ac"` | `"hectares"` | `"ha"`)

## Grid

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