Fix lineSliceAlong() dropping altitude of the line's vertices

CHANGELOG.md

@@ -3,6 +3,7 @@
 Mapbox welcomes participation and contributions from everyone.
 
 ### main
+- Fixed `TurfMisc#lineSliceAlong` dropping the altitude of the line's vertices, a regression introduced in v7.10.0.
 
 ### v7.10.0 - February 05, 2026
 - Added `DirectionsRefreshResponse#fromJson(Reader)`, a static factory method that deserializes a `DirectionsRefreshResponse` from a `java.io.Reader`.

scripts/coverage.sh

@@ -1,9 +1,9 @@
 #!/bin/bash
 set -eoux
 # control sum of the key is const: echo | shasum -a 256 pgp_keys.asc
 shaSumAscKey="d56942c32a1bb70af75bf972302b6114049fb59cb76193fac349bb9b587b60c2"
 
-curl https://keybase.io/codecovsecurity/pgp_keys.asc -o pgp_keys.asc
+curl https://uploader.codecov.io/verification.gpg -o pgp_keys.asc
 # check sum
 echo "$shaSumAscKey  pgp_keys.asc" | shasum -a 256 -c
 
@@ -21,4 +21,4 @@
 shasum -a 256 -c codecov.SHA256SUM
 
 chmod +x codecov
-./codecov
+./codecov

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

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

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

@@ -583,6 +583,27 @@ public void testLineAlongStopLongerThanLength() throws IOException, TurfExceptio
             lineCoordinates.get(lineCoordinates.size() - 1).flattenCoordinates(), DELTA);
   }
 
+  @Test
+  public void testLineSliceAlongPreservesAltitude() throws TurfException {
+    List<Point> input = Arrays.asList(
+      Point.fromLngLat(113.99414062499999, 22.350075806124867, 10.0),
+      Point.fromLngLat(115.0, 22.8, 20.0),
+      Point.fromLngLat(116.76269531249999, 23.241346102386135, 30.0));
+    LineString line = LineString.fromLngLats(input);
+
+    // Slicing the whole line means every returned point is an original vertex.
+    double stop = TurfMeasurement.length(line, TurfConstants.UNIT_MILES);
+    LineString sliced = TurfMisc.lineSliceAlong(line, 0, stop, TurfConstants.UNIT_MILES);
+
+    List<Point> slicedCoordinates = sliced.coordinates();
+    assertEquals(input.size(), slicedCoordinates.size());
+    for (int i = 0; i < input.size(); i++) {
+      assertTrue("point " + i + " lost altitude", slicedCoordinates.get(i).hasAltitude());
+      assertArrayEquals(input.get(i).flattenCoordinates(),
+              slicedCoordinates.get(i).flattenCoordinates(), DELTA);
+    }
+  }
+
   @Test
   public void testShortLine() throws IOException, TurfException {