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Fix incorrect open linestring distance computation #1499

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Merged
michaelkirk merged 2 commits into from
Feb 4, 2026
+35 −2
Merged

Fix incorrect open linestring distance computation #1499

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b1da187
Fix incorrect open linestring distance computation
Kontinuation Feb 4, 2026
a4b52bc
Add changelog entry for LineString distance fix
Kontinuation Feb 4, 2026
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2 changes: 2 additions & 0 deletions geo/CHANGES.md
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Original file line number Diff line number Diff line change
Expand Up @@ -11,6 +11,8 @@
- <https://github.com/georust/geo/pull/1490>
- Add Voronoi diagram generation functionality
- <https://github.com/georust/geo/pull/1487>
- Fix Euclidean distance fast path for open `LineString`s to consider the last vertex (avoids incorrect `LineString`-to-`LineString` distances for separable geometries).
- <https://github.com/georust/geo/pull/1499>

## 0.32.0 - 2025-12-05

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35 changes: 33 additions & 2 deletions geo/src/algorithm/line_measures/metric_spaces/euclidean/distance.rs
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Expand Up @@ -708,9 +708,17 @@ fn calculate_vertex_intercepts<F: GeoFloat>(
perpendicular_slope: F,
use_x_intercept: bool,
) -> Vec<ProjectedVertex<F>> {
// Skip the last coordinate as it duplicates the first in closed polygon rings.
// If this is a closed ring (polygon exterior/interior), skip the duplicate closing vertex.
// For open LineStrings, we must include the last vertex; otherwise the fast path can miss
// the true nearest neighbour.
// We maintain the original index for later segment construction.
coords[..coords.len().saturating_sub(1)]
let is_closed = coords.first() == coords.last();
let coords = if is_closed {
&coords[..coords.len().saturating_sub(1)]
} else {
coords
};
coords
.iter()
.enumerate()
.map(|(idx, &coord)| {
Expand Down Expand Up @@ -854,6 +862,7 @@ mod test {
let zero_dist = line_segment_distance(p1, p1, p2);
assert_relative_eq!(zero_dist, 0.0);
}

#[test]
// Point to Polygon, outside point
fn point_polygon_distance_outside_test() {
Expand Down Expand Up @@ -1339,6 +1348,28 @@ mod test {
assert_relative_eq!(Euclidean.distance(&ls, &line), 1.0);
}

#[test]
fn test_linestring_linestring_distance() {
let ls1: LineString<f64> =
LineString::from(vec![(-13.242, 2.942), (-27.982, -18.803), (-6.811, -4.642)]);
let ls2: LineString<f64> = LineString::from(vec![
(18.297, 31.208),
(29.368, 30.533),
(26.45, 0.543),
(14.711, -1.764),
]);

let rect_a = ls1.bounding_rect().unwrap();
let rect_b = ls2.bounding_rect().unwrap();
let x_separated = rect_a.max().x < rect_b.min().x || rect_b.max().x < rect_a.min().x;
let y_separated = rect_a.max().y < rect_b.min().y || rect_b.max().y < rect_a.min().y;
assert!(x_separated || y_separated);

let expected = 21.713575661323034_f64;
let d = Euclidean.distance(&ls1, &ls2);
assert_relative_eq!(d, expected, epsilon = 1e-12);
}

#[test]
// Triangle-Point test: point on vertex
fn test_triangle_point_on_vertex_distance() {
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