Skip to content

Fix off-by-one indexing bug in DouglasPeucker simplify #387

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Open
asinghvi17 wants to merge 1 commit into
base: main
Choose a base branch
from
Open

Fix off-by-one indexing bug in DouglasPeucker simplify #387

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
2 changes: 1 addition & 1 deletion src/transformations/simplify.jl
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -301,7 +301,7 @@ function _simplify(alg::DouglasPeucker, points::Vector, preserve_endpoint)
i = 2 # already have first and last point added
start_idx, end_idx = 1, npoints
max_idx, max_dist = _find_max_squared_dist(points, start_idx, end_idx)
while i ≤ min(MIN_POINTS + 1, max_points) || (i < max_points && max_dist > max_tol)
while i < min(MIN_POINTS + 1, max_points) || (i < max_points && max_dist > max_tol)
Copy link
Member

@evetion evetion Feb 2, 2026

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

This is a fix, but I'm not sure what it means in terms of the algorithm (should MIN_POINTS + 1 become MIN_POINTS?). There's also preserve_endpoint that extends the length with 1 when true, does that matter here?

# Add next point to results
i += 1
results[i] = max_idx
Expand Down
12 changes: 12 additions & 0 deletions test/transformations/simplify.jl
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -21,6 +21,18 @@ datadir = realpath(joinpath(dirname(pathof(GO)), "../test/data"))
end

@testset "DouglasPeucker" begin
# Test for issue #386: BoundsError when simplifying small geometries with low number/ratio
@testset "small geometry simplification (issue #386)" begin
# This would cause a BoundsError before the fix due to indexing bug in the while loop
line = GI.LineString([(rand(), rand()) for _ in 1:4])
@test_nowarn GO.simplify(line; ratio=0.1)
@test_nowarn GO.simplify(line; tol=0.1)
@test_nowarn GO.simplify(line; number=3)
# Verify the output is valid
result = GO.simplify(line; number=3)
@test GI.npoint(result) == 3
end

poly_coords = JLD2.jldopen(joinpath(datadir, "complex_polygons.jld2"))["verts"][1:4]
for c in poly_coords
npoints = length(c[1])
Expand Down
Loading