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Fix lineSliceAlong() dropping altitude of the line's vertices (#1637)
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Lines changed: 42 additions & 5 deletions

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‎CHANGELOG.md‎

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Mapbox welcomes participation and contributions from everyone.
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### main
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- Fixed `TurfMisc#lineSliceAlong` dropping the altitude of the line's vertices, a regression introduced in v7.10.0.
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### v7.10.0 - February 05, 2026
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- Added `DirectionsRefreshResponse#fromJson(Reader)`, a static factory method that deserializes a `DirectionsRefreshResponse` from a `java.io.Reader`.

‎scripts/coverage.sh‎

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@@ -3,7 +3,7 @@ set -eoux
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# control sum of the key is const: echo | shasum -a 256 pgp_keys.asc
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shaSumAscKey="d56942c32a1bb70af75bf972302b6114049fb59cb76193fac349bb9b587b60c2"
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curl https://keybase.io/codecovsecurity/pgp_keys.asc -o pgp_keys.asc
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curl https://uploader.codecov.io/verification.gpg -o pgp_keys.asc
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# check sum
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echo "$shaSumAscKey pgp_keys.asc" | shasum -a 256 -c
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@@ -21,4 +21,4 @@ gpgv codecov.SHA256SUM.sig codecov.SHA256SUM
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shasum -a 256 -c codecov.SHA256SUM
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chmod +x codecov
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./codecov
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./codecov

‎services-turf/src/main/java/com/mapbox/turf/TurfMisc.java‎

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@@ -5,6 +5,7 @@
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import androidx.annotation.Nullable;
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import com.mapbox.geojson.Feature;
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import com.mapbox.geojson.FlattenListOfPoints;
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import com.mapbox.geojson.LineString;
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import com.mapbox.geojson.Point;
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import com.mapbox.turf.models.LineIntersectsResult;
@@ -188,9 +189,11 @@ public static LineString lineSliceAlong(@NonNull LineString line,
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@FloatRange(from = 0) double stopDist,
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@NonNull @TurfConstants.TurfUnitCriteria String units) {
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double[] coords = line.flattenCoordinates().getFlattenLngLatArray();
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FlattenListOfPoints flattenCoordinates = line.flattenCoordinates();
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double[] coords = flattenCoordinates.getFlattenLngLatArray();
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double[] altitudes = flattenCoordinates.getAltitudes();
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int size = line.flattenCoordinates().size();
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int size = flattenCoordinates.size();
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if (size < 2) {
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throw new TurfException("Turf lineSlice requires a LineString Geometry made up of "
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+ "at least 2 coordinates. The LineString passed in only contains " + size + ".");
@@ -203,7 +206,9 @@ public static LineString lineSliceAlong(@NonNull LineString line,
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double travelled = 0;
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for (int i = 0; i < size; i++) {
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Point pointAtI = Point.fromLngLat(coords[i * 2], coords[i * 2 + 1]);
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// Altitude is kept only for the original vertices: the interpolated start and stop points
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// are computed with 2D math (see TurfMeasurement#destination) and have no altitude.
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Point pointAtI = pointAt(coords, altitudes, i);
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if (startDist >= travelled && i == size - 1) {
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break;
@@ -247,6 +252,16 @@ public static LineString lineSliceAlong(@NonNull LineString line,
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return LineString.fromLngLats(slice);
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}
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@NonNull
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private static Point pointAt(@NonNull double[] coords, @Nullable double[] altitudes, int index) {
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double longitude = coords[index * 2];
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double latitude = coords[(index * 2) + 1];
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if (altitudes != null && !Double.isNaN(altitudes[index])) {
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return Point.fromLngLat(longitude, latitude, altitudes[index]);
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}
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return Point.fromLngLat(longitude, latitude);
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}
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/**
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* Takes a {@link Point} and a {@link LineString} and calculates the closest Point on the
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* LineString.

‎services-turf/src/test/java/com/mapbox/turf/TurfMiscTest.java‎

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lineCoordinates.get(lineCoordinates.size() - 1).flattenCoordinates(), DELTA);
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}
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@Test
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public void testLineSliceAlongPreservesAltitude() throws TurfException {
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List<Point> input = Arrays.asList(
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Point.fromLngLat(113.99414062499999, 22.350075806124867, 10.0),
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Point.fromLngLat(115.0, 22.8, 20.0),
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Point.fromLngLat(116.76269531249999, 23.241346102386135, 30.0));
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LineString line = LineString.fromLngLats(input);
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// Slicing the whole line means every returned point is an original vertex.
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double stop = TurfMeasurement.length(line, TurfConstants.UNIT_MILES);
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LineString sliced = TurfMisc.lineSliceAlong(line, 0, stop, TurfConstants.UNIT_MILES);
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List<Point> slicedCoordinates = sliced.coordinates();
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assertEquals(input.size(), slicedCoordinates.size());
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for (int i = 0; i < input.size(); i++) {
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assertTrue("point " + i + " lost altitude", slicedCoordinates.get(i).hasAltitude());
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assertArrayEquals(input.get(i).flattenCoordinates(),
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slicedCoordinates.get(i).flattenCoordinates(), DELTA);
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}
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}
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@Test
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public void testShortLine() throws IOException, TurfException {
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