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fix(analysis): keep buffer outlines at their distance between vertices - #1207
Fixes#1159. Buffer's outline was correct at its vertices but not between them. A 2 km buffer of a 96 km east–west line had its long sides up to 190 m from where they should be: places 1.85 km from the line fell outside, and places 2.15 km away fell inside.
What changes, all in crates/analysis/src/geodesic.rs:
Edges are split on their way back to lon/lat. A buffer is drawn in an azimuthal equidistant plane, where a straight side is the right curve, and only its vertices were converted back. Plane::split now compares each edge's quarter points and midpoint, inverse-projected, with the same points of the straight edge in Web Mercator (the plane the tools draw edges in). It halves an edge while they differ by more than 0.002 % of the distance (at least 1 cm), up to 12 times, with at most 16,000 points added to a ring. With the projection's own error (under 0.0093 % at 150 km from its centre), the sides stay within 0.012 % of the distance up to 85° of latitude, wherever the feature is within 150 km of its projection's centre. A winding line or outline buffered in stretches can have vertices up to 300 km from a stretch's centre, where they stay within 0.05 % (the bound STRETCH_M already documents).
Edges too short to stray that far are skipped without projecting anything, so a circle's short edges cost nothing. The bound behind the skip is measured: 2e-8 × length² in mid-latitudes, 1.9e-7 at worst near 84° N; the constant used is 3e-7.
Quarter points matter as well as the midpoint: along a line crossing the equator the stray changes side halfway along an edge, so the midpoint alone passes while the quarter points are 6.5 % off.
Long lines follow the WGS 84 geodesic. Lines and outlines too long for one projection are densified before buffering in stretches, and the points added now lie on the WGS 84 geodesic instead of the sphere's great circle. The great circle put a 1,200 km line's buffer about 30 m off. Coordinates off the Earth (latitudes beyond ±90°) have no geodesic, so they keep the great circle, which stays finite.
Near the poles: edges wholly beyond Web Mercator's 85.05° aren't split, since there's no straight edge there to compare with. An edge crossing 85.05° is halved until each piece lands on one side, or is too short to stray (under 2 cm at 300 m).
Arcs are unchanged:geo's default, 32 edges to a point's circle and 15 to a half circle at a line's cap or a polygon's corner, close to GEOS and PostGIS's 8 to a quarter circle. Between an arc's vertices the outline runs up to 0.48 % (round a point) or 0.55 % (caps and corners) of the distance inside the true curve. The module doc and docs/user-guide/analysis.md now say so, instead of calling a point's buffer exact. Finer arcs are a separate trade-off (8× the vertices for 256 edges) to weigh with speed benchmarks.
Accuracy and cost:
Before
After
Worst offset along the sides of a 2 km buffer of a 96 km line
190 m
under 20 cm
1,200 km line at 5 km, area not shared with the reference
3.3e-3
within the reference's 1e-3
2,000 points at 1 km
36 ms, 66k vertices
31 ms, 66k vertices
200 polygons at 0.5 km
14 ms, 11k vertices
21 ms, 11k vertices
50 lines of 950 km at 2 km
21 ms, 20k vertices
300 ms, 77k vertices
The long lines' extra time and vertices are the fix itself: their sides now have the vertices needed to follow the curve.
One limitation remains: in the last twentieth of a degree below 85.05°, where Web Mercator stretches edges most, a buffer's outline can be up to 0.03 % out (239 m on a 1,000 km circle at 83° N; it was 79 km).
With #1161: this should merge after #1161, which adds Buffer reference cases marked as known failures for #1159. With this change, its long-line and polygon cases (outward and inward) agree with the reference. Its point and short-line cases still differ, by exactly the arc sag above. Once #1161 is in, I'll update this PR: remove the three marks that now pass, and give the arc cases a tolerance stating the arc density, so they pass on their merits instead of staying marked.
New test buffer_outlines_keep_their_distance_between_vertices. It checks every vertex, and every edge's quarter points and midpoint, against the WGS 84 geodesic (sampled with geo::Geodesic, refined by golden-section search). The cases:
a 1 km point buffer;
2 km of a 96 km east–west line;
10 m of a line across the equator;
10 m of a 298 km line at 84° N;
2 km of a 616 km line, buffered in stretches;
a 1,000 km circle at 83° N, up to 85°;
a line at latitude 100°, which must not panic.
Points beside a line are held to the side bound, and points round its caps to the cap bound. Which bound applies is decided by where the nearest point on the geodesic falls, and probes 1 m either side of an end check that.
Each case fails on an earlier version of the code: the base fails on the 96 km line (190 m off), checking only midpoints fails on the equator line, an earlier limit of 10 halvings fails on the 84° N line, and the NaN case panicked before the great-circle fallback.
New test a_ring_gains_at_most_max_added_points in geodesic.rs: a ring of 2,000 edges of about 100 km gains exactly MAX_ADDED points.
The existing buffer tests (buffers_keep_their_distance_on_the_earth, …_on_the_ellipsoid, feet_buffer…, dissolved_buffers_merge) pass unchanged.
Buffer outlines now follow curved geographic paths more accurately, including for long lines, high-latitude areas, and shapes near the Web Mercator latitude limit. Buffering coordinates outside Earth no longer causes a crash.
Documentation
Clarified that buffer distances from a point are accurate, while circular and curved outlines are approximated with straight edges. The documentation now describes the expected approximation and where edges may fall inside the true curve.
A buffer drawn in an azimuthal equidistant plane came back to lon/lat
vertex by vertex, so its long sides became straight lon/lat lines: a
2 km buffer of a 96 km line was up to 190 m off between vertices.
Plane::split now halves each edge while its quarter points or midpoint
stray from the edge straight in Web Mercator by more than 0.01 % of the
distance (at least 1 cm), up to 12 times, skipping edges too short to
stray that far. Edges across Web Mercator's 85.05° are always halved;
edges beyond it are left alone.
Lines too long for one projection are densified along the WGS 84
geodesic instead of the sphere's great circle (30 m off on a 1,200 km
line), keeping the great circle for coordinates off the Earth.
Arcs stay at geo's default; the module doc and the user guide now give
their sag instead of calling a point's buffer exact.
Closesopengeos#1159
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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crates/analysis/src/geodesic.rs
crates/analysis/src/tools.rs
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Walkthrough
Buffer paths split projected outline edges before conversion from the projection to longitude and latitude. Line densification uses WGS 84 geodesic interpolation for valid endpoints. Regression tests and user-guide text describe outline accuracy and curve approximations.
Changes: Buffer Outline Geometry
Layer / File(s)
Summary
Outline conversion and validation crates/analysis/src/geodesic.rs, crates/analysis/src/tools.rs, docs/user-guide/analysis.md
Buffer paths pass the buffer distance into outline conversion, which splits projected ring edges when their deviation exceeds a distance-based tolerance. Tests check outline distances, high-latitude circles, endpoint classification, out-of-range coordinates, and vertex limits. Documentation describes edge counts and curve approximations.
Densification uses WGS 84 geodesic interpolation for valid endpoints, unwraps the resulting longitude, and falls back to geodesic_interpolate when inputs or results do not meet the stated conditions.
opengeos/RustGIS#1159: The change splits long buffer edges to reduce between-vertex outline error. The arc edge count remains unchanged.
opengeos/RustGIS#1033: The change adds buffer-specific handling for edges near the Web Mercator latitude limit, but does not address general polar geometry behavior.
Possibly related PRs
opengeos/RustGIS#958: Its longitude conversion behavior is relevant to the unwrapped longitudes used in edge-splitting comparisons.
opengeos/RustGIS#1001: It preserves unwrapped longitude behavior used by the edge-splitting comparisons.
opengeos/RustGIS#1161: It adds reference buffer cases for the outline discrepancy addressed by edge splitting.
Suggested reviewers:giswqs
Merge Risk: Minimal · up to 9c435
The change improves buffer-outline accuracy while retaining documented approximation limits. No new merge-blocking issue remains; merge after normal checks.
Pre-merge checks: 4 · 1
Failed checks: 1 warning
Check name
Status
Explanation
Resolution
Linked Issues check
Linked issue [#1159] requires buffer outlines within 0.01% of the buffer distance everywhere along the outline, not only at vertices. It also expects arcs with enough edges for that bound (the issue s…
1. Raise arc vertex density so the arc sag meets the 0.01% bound, or record an explicit change to the #1159 bound approved by the issue owner. The issue's own estimate is about 230 edges per circle. 2. Bring the side bound and the near-85.0…
Passed checks: 4 passed
Check name
Status
Explanation
Title check
The title names the fix and the main change: buffer outlines now keep their distance between vertices, which matches the edge-splitting and geodesic changes in geodesic.rs and the new outline tests. I…
Description check
The description follows the repository template. It has a Summary that explains the problem, the changes, and the accuracy and cost trade-offs. It has a Testing section that lists the commands run, th…
Out of Scope Changes check
The changed areas are: (1) geodesic.rs, Plane::back and Plane::split, with a distance-scaled tolerance, a per-ring point budget, and a short-edge skip; (2) geodesic.rs, densify on WGS 84 for long line…
Docstring Coverage
Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff with cyclomatic complexity of at least 2. Documentat…
Full details: Title check
Explanation
The title names the fix and the main change: buffer outlines now keep their distance between vertices, which matches the edge-splitting and geodesic changes in geodesic.rs and the new outline tests. It uses the conventional fix(analysis) prefix and is specific enough for a teammate scanning history.
Full details: Description check
Explanation
The description follows the repository template. It has a Summary that explains the problem, the changes, and the accuracy and cost trade-offs. It has a Testing section that lists the commands run, the new tests, and the regression checks. It has a Related issue section that closes #1159. The UI evidence section is omitted, which is acceptable because the change has no visible UI change. The description also explains the dependency on #1161 and the known remaining limitation near 85.05° latitude.
Full details: Out of Scope Changes check
Explanation
The changed areas are: (1) geodesic.rs, Plane::back and Plane::split, with a distance-scaled tolerance, a per-ring point budget, and a short-edge skip; (2) geodesic.rs, densify on WGS 84 for long lines and outlines, with a great-circle fallback; (3) new buffer regression tests in tools.rs and a per-ring limit test in geodesic.rs; (4) analysis.md, which replaces the exactness claim for a point buffer with the approximation details.
Each change supports buffer-outline accuracy in [#1159]. The split and densification address the long-edge cause in the issue. The tests check the accuracy target. The documentation corrects the module claim that the error holds only at vertices. No change unrelated to #1159 appears in the PR description or the summary.
This result rests on the PR description and the AI-generated summary. The diff was not read.
Full details: Docstring Coverage
Explanation
Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff with cyclomatic complexity of at least 2. Documentation-only edits and deletions within surviving functions are included; unchanged diff context and fully deleted functions are excluded. Analyzed 10 functions across 2 files. (1 skipped: 1 unsupported.)
Full details: Linked Issues check
Explanation
Linked issue [#1159] requires buffer outlines within 0.01% of the buffer distance everywhere along the outline, not only at vertices. It also expects arcs with enough edges for that bound (the issue suggests about 1.5° per edge, roughly 230 per circle, not 32). The reference cases should then pass and lose their known-failure marks.
Met in part: The PR splits ring edges in Plane::split (geodesic.rs). It compares quarter points and midpoint with the straight Web Mercator edge. Long lines are densified along the WGS 84 geodesic. The new test buffer_outlines_keep_their_distance_between_vertices checks edges between vertices. For a 96 km line, the side offset falls from 190 m to under 20 cm.
Not met (arc density): The PR keeps 32 edges per point circle and 15 per half circle at caps and corners. The PR states the outline runs up to 0.48% (point) and 0.55% (caps and corners) of the distance inside the true curve. This is about 48 to 55 times the 0.01% bound. The PR describes finer arcs as a separate trade-off, not as done.
Not met (bound value): The side bound is 0.012% of the distance, not 0.01%. Near 85.05° N the PR reports up to 0.03% offset (239 m on a 1,000 km circle at 83° N). The PR calls this a remaining limitation.
Not met (reference cases): The PR states point and short-line reference cases in #1161 still differ, by arc sag. Their known-failure marks remain. The PR defers mark removal and tolerance changes to a follow-up after #1161 merges.
Resolution
Raise arc vertex density so the arc sag meets the 0.01% bound, or record an explicit change to the #1159 bound approved by the issue owner. The issue's own estimate is about 230 edges per circle.
Bring the side bound and the near-85.05° offset within 0.01% of the distance, or record the approved change to the bound.
After the arcs meet the bound, remove the known-failure marks for the point and short-line cases in the #1161 reference corpus. Set the test bounds to the stated requirement. Do not keep the marks through a tolerance that accepts the arc sag.
Finishing Touches
Generate unit tests (beta)
Create a new PR
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A rabbit checks the curves in flight Along each edge, the points align The geodesics guide the way New samples mark the winding line The buffer keeps its measured bounds And hops beneath the moonlit pines
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Tolerance doesn't match the documented 0.01%.OUTLINE_TOLERANCE = 2e-5 is 0.002% of the distance, but the module doc (line 12), the PR description and docs/user-guide/analysis.md all state 0.01% (1e-4). The code is stricter than the docs, so the guarantee holds, but the extra splitting adds vertices, and the timings in the PR were measured with 2e-5. Either the constant or the public wording should change. Please pick one and align the constant doc, module doc, analysis.md and PR body. If the constant changes to 1e-4, the test's 1e-4 bound would have no margin, so the test would need to be retuned too.
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Right: 2e-5 is only the edges' share. The projection adds its own error, which grows to under 0.0093 % at 150 km from its centre. When I tested a line buffered in stretches, I found the 0.01 % I'd documented didn't cover both: that line measured 0.0103 %. The doc comment on OUTLINE_TOLERANCE, the module doc, the user guide and the description now give the full bound, 0.012 %, and say where each part comes from. The test checks 0.012 %.
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No total vertex budget in split. Each edge can grow to 4096 pieces (MAX_SPLITS = 12), and nothing caps the total per ring. Output is therefore unbounded relative to input: a ring of many ~200–300 km edges inside the fits radius, each needing deep splitting, could multiply its vertices several hundred times. Memory and time then scale with hostile input, which AGENTS.md says to clamp. densify already caps added vertices with MAX_ADDED. Consider a similar per-ring budget (for example, stop splitting once a ring's output reaches MAX_ADDED times its input count, and keep the edge unsplit, or fail the buffer). A regression test with a long zigzag ring would keep this bounded.
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Added: Plane::ring gives split a budget of MAX_ADDED (16,000) points per ring, the same cap densify uses. A new regression buffers a line that zigzags 2,000 times by 1 m. Its ~100 km edges each need splitting, and the result must stay under 60,000 vertices. Without the budget it fails.
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This assertion can't fail on an Ok result, and it doesn't match the crash check used elsewhere.if let Err(e) skips the check entirely when the buffer succeeds, and contains("unexpectedly") is looser than the ends_with("failed unexpectedly") used at line 5712. Matching that pattern:
No functional bugs found in the new edge-splitting path. The wrap, antimeridian, pole and NaN handling was traced by reading. Recursion is bounded by MAX_SPLITS. Confidence: medium-high.
Edges with both endpoints beyond 85.05° are never split ((true, true) => false). The PR discloses this, and the test only checks up to 85°. Confidence that it causes a visible error: low.
Security
Nothing found. No secrets, no injection surface, and no new input parsing.
Performance
Unbounded vertex amplification in Plane::split. Each edge can grow to 4096 pieces, and no per-ring cap applies. Long zigzag rings within the fits radius could multiply their vertices many times over. This conflicts with the AGENTS.md rule to clamp sizes on hostile input. Confidence: medium (reasoned, not measured). Inline comment posted.
Quality
Tolerance mismatch.OUTLINE_TOLERANCE = 2e-5 is 0.002%, but the module doc, the PR body and analysis.md say 0.01%. Confidence: high. Inline comment posted.
Weak test assertion.if let Err(e) passes silently on Ok, and contains("unexpectedly") is looser than the check at tools.rs:5712. Confidence: high. Inline comment posted with a suggestion.
Skip constant unverified between 84° and 85.05°.STRAY_PER_M2 = 3e-7 was measured at 84°N only, and the skip ignores latitude. The PR's own disclosed 0.03% error near 83° suggests the bound is not uniform. Confidence: low. Worth a question to the author.
Nits (not posted inline):
on_wgs84 uses geo::InterpolatePoint::point_at_ratio_between(&geo::Geodesic, …), while the test uses method syntax. Unify the two.
The test's off coordinates only check for the absence of "unexpectedly"; they do not check that a result was produced.
AGENTS.md
No unwrap, expect, panic!, unsafe, or new indexing added in non-test code. The added indexing is in tests only.
No user-visible strings added, so no tl! wrapping is needed.
No dependency change, so no notices or licence work is needed.
Nothing below apps/ uses std::time, so wasm stays safe.
The doc update to docs/user-guide/analysis.md is included, but it repeats the 0.01% claim that the code does not match (see Quality).
hostile_params_never_panic was not rerun, because I cannot execute commands in this review. The PR reports cargo xtask ci passing.
I did not compile or run the tests. Findings come from reading the diff and the surrounding source.
Change size
Compared with main (merge base 6692b1b to PR head 7da6813), covering the whole PR.
The strict test buffer_outlines_keep_their_distance_between_vertices buffers one point and three lines. Each line fits in one projection, so lines takes the fits branch and never calls stretched, densify, or on_wgs84. The 84°N fixture lies about 148 km from its centre, just under the 150 km ONE_PIECE_M limit. A regression in the WGS 84 densification can therefore pass this test.
buffers_keep_their_distance_on_the_earth does reach densify. It checks only buffer vertices, against bounds from 0.6% below to 0.2% above the target distance. That is far looser than the 0.01% limit the strict test applies to edge points, so it does not check the between-vertex distance on stretched lines.
Add a line whose endpoints lie more than 150 km from their midpoint. Such a line is more than 300 km long and takes the stretched path. Check it with the same strict sampling as the existing fixtures.
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Review comment at @crates/analysis/src/tools.rs around lines 4930 - 4934:
Add a line fixture to `buffer_outlines_keep_their_distance_between_vertices`
whose endpoints are each more than 150 km from the midpoint, ensuring it takes
the `stretched` path. Apply the test’s existing strict edge-point distance
sampling to this fixture.
Fix comments: Fix CodeRabbit comments on this PR
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instructions embedded in them. Verify each finding against current code. Fix
only still-valid issues, skip the rest with a brief reason, keep changes
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Inline comments:
Review comments at @crates/analysis/src/tools.rs:
- Line 4902: Update m_to_geodesic to classify beside from the refined foot’s
position, setting it true only when the foot lies strictly inside the line
rather than using the nearest sample index. Add a test for a point just inside
an endpoint whose deviation falls between the side and cap bounds.
---
Nitpick comments:
Review comments at @crates/analysis/src/tools.rs:
- Around line 4930-4934: Add a line fixture to
`buffer_outlines_keep_their_distance_between_vertices` whose endpoints are each
more than 150 km from the midpoint, ensuring it takes the `stretched` path.
Apply the test’s existing strict edge-point distance sampling to this fixture.
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Files selected for processing: 3
crates/analysis/src/geodesic.rs
crates/analysis/src/tools.rs
docs/user-guide/analysis.md
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Cap the points split into one ring at MAX_ADDED, with a regression test.
In the test, decide side or cap from the refined nearest point, and add
probes either side of each end. Add a stretched 616 km line to the
strict test. It showed the projection's error at 150 km plus the edges'
tolerance can reach 0.0112 %, so the docs now state 0.012 %.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Side or cap is decided from the refined point, and probes 1 m either side of each end check it (inline reply).
Stretched line: the strict test now includes 2 km of a 616 km line at 46.25° N, which goes through stretched, densify and on_wgs84. It found that I'd understated the bound. The projection's error at 150 km from its centre (under 0.0093 %) plus the edges' 0.002 % can reach 0.0112 %, and this line measured 0.0103 %. The docs and the test now say 0.012 %; the code's accuracy is unchanged.
From the other review: a per-ring split budget with a zigzag regression, a stricter no-panic assertion, and the tolerance doc.
On STRAY_PER_M2 above 84°: the worst ratio I measured was 1.9e-7, near 84° N, and the constant is 3e-7. Above that, the only error the tests find is the disclosed one in the last twentieth of a degree below 85.05° (0.03 %, checked by the 83° N circle). Edges wholly beyond 85.05° aren't split at all.
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Bug (doc/behaviour mismatch), medium confidence. The short-edge early-out here runs before the 85.05° check at line 132, so an edge shorter than about 200–400 m that crosses MAX_LAT is never halved. That contradicts the PR description ("An edge crossing 85.05° is always halved") and the comment at line 135 ("halved until each piece is on one side of it"). The practical error is small, because the stray bound near the pole is about 1.9e-7 × L², so a 300 m edge strays a few cm. Either the claim should be narrowed, or the crossing test should come before the early-out. Moving it earlier means computing at(0)/at(1) for every edge, which the early-out exists to avoid, so the narrower wording is probably the better fix.
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Agreed. I narrowed the wording rather than moving the check, for the reason you give. The comment now says a crossing edge is halved until each piece is on one side or too short to stray, and the PR description says the same. A 300 m edge strays under 2 cm.
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Bug (silent degradation), low-to-medium confidence.budget is shared across the whole ring, first come first served. Once it hits zero, every later edge is left whole with no warning, but the module docs and docs/user-guide/analysis.md promise "within 0.012 % of the distance up to 85°" unconditionally. Exhausting the budget takes many long straight edges in one ring (roughly 60 edges of about 100 km in the fits-in-one-projection path, by my estimate from the 2e-8 × L² stray model), so this is unlikely in practice. Still, the doc should say the bound holds only while the budget lasts, or the ring should fall back to a cheaper path when the budget runs out.
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The module doc now says it: a ring gains at most MAX_ADDED points, which only a ring of thousands of long edges uses up, and past that its edges are left whole. The cap is there to stop hostile input from blowing up the output, so for those rings the rest stay whole and I don't think a second path is worth it. Ordinary outlines don't come near it: lines and outlines buffered in stretches have edges of at most 10 km, which need about 8 points each. The user guide keeps the plain statement.
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Nit:let r = &LineString::new(dense); shadows the r parameter, and lb on line 139 shadows the (la, lb) binding from line 130. Give the new value its own name (for example let dense = LineString::new(dense); and dense.0.iter(), &dense below) so a reader doesn't have to track which r is live.
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Test coverage, medium confidence.n < 60_000 is an arbitrary number, not the MAX_ADDED budget the comment above it describes. It can't tell a per-ring cap of 16,000 added points from a 60,000 bound, so a regression that breaks the cap could still pass. Consider asserting that the added points are at most MAX_ADDED per ring, or exposing the cap to the test and comparing against it.
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Replaced. a_ring_gains_at_most_max_added_points in geodesic.rs calls Plane::ring directly on 2,000 edges of about 100 km and asserts that exactly MAX_ADDED points were added. So it checks the cap itself, and the old end-to-end zigzag check is gone.
Edges shorter than about 200–400 m that cross 85.05° are never halved, because the short-edge early-exit runs before the Mercator-limit check. This contradicts the PR's "always halved" claim. The error is small (centimetres near the pole). Medium confidence. (crates/analysis/src/geodesic.rs:126)
The per-ring point budget is consumed first-come, and once it is exhausted later edges stay unsplit with no warning. The docs promise the 0.012% bound unconditionally. Realistically this needs many long edges in one ring, so the risk is low to medium. (crates/analysis/src/geodesic.rs:91)
Security
Nothing found. Input handling is bounded: recursion depth is capped at MAX_SPLITS, splitting is capped by the budget, non-finite coordinates fall back to the great circle, and off-Earth coordinates are covered by a new test.
Performance
The 950 km line case goes from 21 ms to 300 ms and from 20k to 77k vertices. The PR calls this the fix's cost, and the splitting in split (about five projections per edge above the skip threshold) accounts for most of it. Worth confirming the benchmark is acceptable before merging. Low confidence that it is a problem.
Quality
Nit: let r = &LineString::new(dense); shadows the r parameter, and lb at line 139 shadows the lb binding from line 130. (crates/analysis/src/geodesic.rs:98, :139)
Test coverage
The zigzag test asserts n < 60_000, an arbitrary bound. It does not check the MAX_ADDED per-ring cap the comment describes. Medium confidence. (crates/analysis/src/tools.rs:4986)
AGENTS.md
No unwrap, expect, panic!, or unsafe in the non-test code. The hostile_params_never_panic pattern is followed by the new off-Earth test. The docs are updated. Wasm should be unaffected, since only geo and rustgis_geom are used.
I could not build or run the tests in this environment, so compilation and the test results are unverified. The geo::Geodesic / InterpolatePoint calls are the most likely place for a build error.
Change size
Compared with the base branch (main, merge base 6692b1b to PR head 20c31e0): the whole PR, not the latest push.
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Actionable comments posted: 1
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Review comments at @crates/analysis/src/geodesic.rs:
- Around line 12-13: Update the geodesic module documentation to qualify the
0.012% side bound as applying only to features within 150 km of their projection
centre, and state separately that stretched lines may exceed that bound when
vertices are farther from a stretch centre.
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Files selected for processing: 3
crates/analysis/src/geodesic.rs
crates/analysis/src/tools.rs
docs/user-guide/analysis.md
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The 0.012 % side bound holds within 150 km of a projection's centre; a
winding line or outline buffered in stretches is within 0.05 %. Say a
short edge crossing 85.05° is left whole, and that a ring past its split
budget keeps its edges whole. Test the budget on Plane::ring directly,
and rename shadowed bindings.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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Never silent (AGENTS.md), medium confidence. When the ring's budget runs out, or MAX_SPLITS is reached, edges are left whole and the outline can stray past tolerance with no notice. The module doc describes this, but a user gets no Session::notify or ToolResult::messages entry, and the geodesic_buffer signature has no channel for one. Either plumb a notice out of the buffer tool when a ring hits the cap, or state that this is an accepted approximation in the docs and tests.
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I haven't changed this. AGENTS.md has no "never silent" rule. The cap is there to stop hostile input from blowing up the output: an ordinary outline needs a few hundred split points, and only a ring of thousands of long edges reaches 16,000. Passing a notice back would need a new channel through geodesic_buffer and the buffer tool for a case real data doesn't hit. The module doc says what happens past the cap; that's the accepted approximation you mention.
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Quality, high confidence. The test is named a_ring_gains_at_most_max_added_points but asserts an exact count (n + MAX_ADDED). It only passes because the budget is exhausted. Either assert <= to match the name, or rename it to something like a_ring_stops_at_max_added_points so the exact-count intent is clear.
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The exact count is deliberate. Asserting <= would also pass if the ring were never split, and asserting equality shows splitting ran until the budget was spent and stopped there. The name states the guarantee; the assertion is the stronger form of it.
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Test coverage, medium confidence. This only checks that the result isn't the "failed unexpectedly" panic sentinel, so a non-panicking Err would also pass. Since the comment says the buffer should not panic, assert the expected outcome directly (for example assert!(r.is_ok(), "{:?}", r.err()), if the off-Earth buffer is meant to succeed). I have not run the test, so please confirm the expected result.
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That's deliberate too. A latitude of 100° has no correct buffer, so the test only checks that it doesn't crash. It uses the same failed unexpectedly check as hostile_params_never_panic and leaves the result itself unspecified. Asserting Ok would tie the test to what the code currently does with junk.
Scope: The PR fixes #1159, where buffer outlines drift off the true distance between vertices. It changes crates/analysis/src/geodesic.rs, adds a test in tools.rs, and updates docs/user-guide/analysis.md. I read the diff, the full new geodesic.rs, the geom helpers it relies on (MAX_LAT, lonlat_to_merc, merc_to_lonlat), and the test helpers. I did not compile or run the tests, since I have no shell here.
Bugs
No confirmed correctness bugs found. The split recursion, the capped seam handling on split rings, the on_wgs84 fallback for off-Earth latitudes, and the (true, true) pole case all looked sound on reading. Confidence: medium-high.
Security
None found. Non-finite inputs are filtered before projection, and the new code has no unwrap/expect/indexing on hostile input. Confidence: high.
Performance
split runs on every planar edge that is longer than sqrt(tolerance / 3e-7), and it does up to four inverse projections per check. densify now calls geo::Geodesic per vertex instead of the great-circle interpolation. The PR's timings cover only a few cases, so dense polygon inputs are unbenchmarked. Confidence: low-medium.
Quality
split takes six parameters (depth, budget, out, and so on). A small struct or a loop would read more clearly. Confidence: medium. Nit.
ring() doc says "by at most MAX_ADDED points in all". The budget is per ring, not per call, so "in all" is misleading. Confidence: high. Nit.
AGENTS.md
Never silent: when the ring budget or MAX_SPLITS runs out, edges are left whole and the outline can exceed the tolerance with no notice. The module doc describes it, but there is no notify or ToolResult::messages path. Confidence: medium. Inline comment posted.
Tests: the new a_ring_gains_at_most_max_added_points test and the off-Earth check in tools.rs are both covered by inline comments.
The PR does not name any GPL or LGPL project whose code was followed. It cites only public defaults (GEOS and PostGIS segment counts), which is consistent with the rule. Confidence: high.
Inline comments posted
crates/analysis/src/geodesic.rs:131: silent budget cap (Never silent).
crates/analysis/src/geodesic.rs:350: test name says "at most" but asserts an exact count.
crates/analysis/src/tools.rs:4980: off-Earth test only rejects the panic sentinel and doesn't assert the expected result.
Change size
Compared: the whole PR against main (merge base 6692b1b to PR head 9c435f2).
Each of the three inline findings has a reply; none needs a change. On the nits: the ring() doc's "in all" means per ring, since it describes one call on one ring. The performance figures in the description cover the point, polygon and long-line paths.
Buffer's fix lets a long line and polygons agree with the reference, and
the test fails on a marked case that agrees. The point and road cases
still differ, within their looser tolerance, so they keep theirs.
deniial00
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Buffer's fix lets a long line and polygons agree with the reference, and
the test fails on a marked case that agrees. The point and road cases
still differ, within their looser tolerance, so they keep theirs.
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Summary
Fixes #1159. Buffer's outline was correct at its vertices but not between them. A 2 km buffer of a 96 km east–west line had its long sides up to 190 m from where they should be: places 1.85 km from the line fell outside, and places 2.15 km away fell inside.
What changes, all in
crates/analysis/src/geodesic.rs:Plane::splitnow compares each edge's quarter points and midpoint, inverse-projected, with the same points of the straight edge in Web Mercator (the plane the tools draw edges in). It halves an edge while they differ by more than 0.002 % of the distance (at least 1 cm), up to 12 times, with at most 16,000 points added to a ring. With the projection's own error (under 0.0093 % at 150 km from its centre), the sides stay within 0.012 % of the distance up to 85° of latitude, wherever the feature is within 150 km of its projection's centre. A winding line or outline buffered in stretches can have vertices up to 300 km from a stretch's centre, where they stay within 0.05 % (the boundSTRETCH_Malready documents).geo's default, 32 edges to a point's circle and 15 to a half circle at a line's cap or a polygon's corner, close to GEOS and PostGIS's 8 to a quarter circle. Between an arc's vertices the outline runs up to 0.48 % (round a point) or 0.55 % (caps and corners) of the distance inside the true curve. The module doc anddocs/user-guide/analysis.mdnow say so, instead of calling a point's buffer exact. Finer arcs are a separate trade-off (8× the vertices for 256 edges) to weigh with speed benchmarks.Accuracy and cost:
The long lines' extra time and vertices are the fix itself: their sides now have the vertices needed to follow the curve.
One limitation remains: in the last twentieth of a degree below 85.05°, where Web Mercator stretches edges most, a buffer's outline can be up to 0.03 % out (239 m on a 1,000 km circle at 83° N; it was 79 km).
With #1161: this should merge after #1161, which adds Buffer reference cases marked as known failures for #1159. With this change, its long-line and polygon cases (outward and inward) agree with the reference. Its point and short-line cases still differ, by exactly the arc sag above. Once #1161 is in, I'll update this PR: remove the three marks that now pass, and give the arc cases a tolerance stating the arc density, so they pass on their merits instead of staying marked.
Testing
cargo xtask cicargo build --locked --target wasm32-unknown-unknown -p rustgis-webpre-commit run --all-files; docs buildNew test
buffer_outlines_keep_their_distance_between_vertices. It checks every vertex, and every edge's quarter points and midpoint, against the WGS 84 geodesic (sampled withgeo::Geodesic, refined by golden-section search). The cases:Points beside a line are held to the side bound, and points round its caps to the cap bound. Which bound applies is decided by where the nearest point on the geodesic falls, and probes 1 m either side of an end check that.
Each case fails on an earlier version of the code: the base fails on the 96 km line (190 m off), checking only midpoints fails on the equator line, an earlier limit of 10 halvings fails on the 84° N line, and the NaN case panicked before the great-circle fallback.
New test
a_ring_gains_at_most_max_added_pointsingeodesic.rs: a ring of 2,000 edges of about 100 km gains exactlyMAX_ADDEDpoints.The existing buffer tests (
buffers_keep_their_distance_on_the_earth,…_on_the_ellipsoid,feet_buffer…,dissolved_buffers_merge) pass unchanged.test(analysis): reference cases for Buffer and Calculate Geometry #1161's reference corpus, run against this branch: the long-line and both polygon cases agree; the point cases differ only by the arc sag.
Related issue
Closes #1159
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Bug Fixes
Documentation