line interpolate point across MetricSpaces #1321

michaelkirk · 2025-03-04T04:39:59Z

I agree to follow the project's code of conduct.
I added an entry to CHANGES.md if knowledge of this change could be valuable to users.

LineInterpolatePoint is currently Euclidean only. As part of #1216, I wanted to make this functionality work across metric spaces.

// geos
line_interpolate_point(line, 0.8, true)
// georust::geo
Euclidean.interpolate_point_at_ratio_from_start(line, 0.8)

// also:
Haversine.interpolate_point_at_ratio_from_start(line, 0.8)
Geodesic.interpolate_point_at_ratio_from_start(line, 0.8)
Rhumb.interpolate_point_at_ratio_from_start(line, 0.8)

As a bonus, I also wanted to add some (IMO) long missing niceties to the api.

// geos communicates "from end" with a negative distance
line_interpolate_point(line, -0.8, true)
// georust::geo
Euclidean.interpolate_point_at_ratio_from_end(line, 0.8)

// geos communicates "distance" rather than "ratio" by passing in `false`
line_interpolate_point(line, 0.8, false)
// georust::geo
Euclidean.interpolate_point_at_distance_from_start(line, 0.8)

// geos
line_interpolate_point(line, -0.8, false)
// georust::geo
Euclidean.interpolate_point_at_distance_from_end(line, 0.8)

You can use all those methods across metric spaces:

Haversine.interpolate_point_at_ratio_from_end(line, 0.8)
Geodesic.interpolate_point_at_distance_from_start(line, 0.8)
Rhumb.interpolate_point_at_distance_from_end(line, 0.8)
// etc.

The names are admittedly long. It's my own preference to have verbose method names over geos-like "mode" parameters.

Bonus

While working on this, and filling out the deprecations, I found and fixed a bug in LineStringSegmentizeHaversine which was using the legacy LineInterpolatePoint, which was Euclidean only. It's easy to make this kind of mistake, the way we've historically not been very explicit about which metric space an algorithm is for.

michaelkirk · 2025-03-04T04:58:29Z

This is a big PR, but it's overwhelmingly docs and tests, I swear!

michaelkirk · 2025-03-05T00:41:27Z

geo-types/src/geometry/line_string.rs

+    /// assert!(lines.next().is_none());
+    /// ```
+    pub fn rev_lines(&'_ self) -> impl ExactSizeIterator<Item = Line<T>> + '_ {
+        self.0.windows(2).rev().map(|w| {


At first I assumed I wanted to do line_string.lines().rev() but that's not quite what I needed.

For example, given a line string with points a, b, c:

lines(): 1. a->b 2. b->c

lines().rev(): 1. b->c 2. a->b

But what I want is:

rev_lines(): 1. c->b 2. b->a

michaelkirk · 2025-03-05T19:53:28Z

I've just pushed up a bike-shedding commit.

There are two equivalent new APIs:

Euclidean.point_at_ratio_from_start(&line_string, 0.5)
line_string.point_at_ratio_from_start(&Euclidean, 0.5)

Previously, the deprecation pointed you to the first version. I changed that deprecation to now recommend the latter.

I don't think it matters much, but the second version is closer to the existing API, so I think it'll be slightly easier to migrate to.

michaelkirk · 2025-03-10T18:09:18Z

geo/src/algorithm/linestring_segment.rs

-                            segment.line_interpolate_point((length - remainder) / length)?;
-
+                        let endpoint = $metric_space
+                            .point_at_ratio_from_start(&segment, (length - remainder) / length);


This is a bugfix in the case of Haversine

dabreegster

All of this looks clear to me. The API choices are very explicit and nice, better than geos. There's lots of repetition in docs, but I don't see any copy/paste errors in them

dabreegster · 2025-03-21T16:40:34Z

geo/src/lib.rs

@@ -49,6 +49,7 @@
 //! - **[`Bearing`]**: Calculate the bearing between two points.
 //!
 //! - **[`Destination`]**: Calculate the destination point from an origin point, given a bearing and a distance.
+//! - **[`InterpolateLine`]**: Interpolate a `Point` along a `Line` or `LineString`.
 //! - **[`InterpolatePoint`]**: Interpolate points along a line.


I've looked at https://docs.rs/geo/latest/geo/algorithm/line_measures/trait.InterpolatePoint.html and this PR a few times, but I'm still fuzzy on the difference -- is the old trait deprecated?

I deprecated it in this PR: https://github.com/georust/geo/pull/1321/files#diff-1e6b7ec38d282e44d7225459b81fa17d1ca9b7529763d44d0550c303077f6826R9

But your comment made me realize I should remove the deprecated one from these front page docs!

dabreegster · 2025-03-21T16:43:44Z

geo/src/algorithm/line_measures/interpolate_line.rs

+        metric_space: &MetricSpace,
+        ratio: F,
+    ) -> Self::Output {
+        let distance = ratio * metric_space.length(self);


The < start or > end case is handled by the other method, all good

---- algorithm::linestring_segment::test::haversine_segment_length stdout ---- thread 'algorithm::linestring_segment::test::haversine_segment_length' panicked at geo/src/algorithm/linestring_segment.rs:333:13: assert_relative_eq!(Haversine.length(&segment), expected_segment_length, epsilon = 1e-9) left = 300003.0789340123 right = 299799.8099830805

…tart, not (Euclidean) line_interpolate_point

michaelkirk force-pushed the mkirk/line-interpolate-point branch from ba43f1a to af415da Compare March 4, 2025 04:40

michaelkirk force-pushed the mkirk/line-interpolate-point branch 5 times, most recently from a18e16d to d421459 Compare March 4, 2025 18:22

michaelkirk mentioned this pull request Mar 5, 2025

update geo a-b-street/ltn#185

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michaelkirk commented Mar 5, 2025

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michaelkirk commented Mar 10, 2025

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michaelkirk mentioned this pull request Mar 11, 2025

impl Clone and Debug for PreparedGeometry #1324

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michaelkirk force-pushed the mkirk/line-interpolate-point branch from ce5aed9 to 4760cb2 Compare March 18, 2025 19:21

dabreegster approved these changes Mar 21, 2025

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michaelkirk added 3 commits March 21, 2025 09:54

line interpolate point across metric spaces

2089ee5

Fix LineStringSegmentHaversine to use Haversine.point_at_ratio_from_s…

a571260

…tart, not (Euclidean) line_interpolate_point

michaelkirk force-pushed the mkirk/line-interpolate-point branch from 4760cb2 to a571260 Compare March 21, 2025 16:55

michaelkirk added this pull request to the merge queue Mar 21, 2025

Merged via the queue into main with commit f1eecc9 Mar 21, 2025
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michaelkirk deleted the mkirk/line-interpolate-point branch March 21, 2025 17:05

michaelkirk mentioned this pull request Mar 24, 2025

Unify line measurement traits (tracking issue) #1181

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line interpolate point across MetricSpaces #1321

line interpolate point across MetricSpaces #1321

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line interpolate point across MetricSpaces #1321

line interpolate point across MetricSpaces #1321

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michaelkirk commented Mar 4, 2025 • edited Loading

Bonus

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