Skip to content

Stabilize polylabel placement #899

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
Symmetricity wants to merge 2 commits into
base: master
Choose a base branch
from
Open

Stabilize polylabel placement #899

Changes from all commits
Commits
Show all changes
2 commits
Select commit Hold shift + click to select a range
3515d21
Stabilize polylabel centroid seed
Symmetricity May 18, 2026
f85385b
Stabilize polylabel queue ties
Symmetricity May 18, 2026
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
22 changes: 16 additions & 6 deletions include/polylabel.h
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -111,18 +111,24 @@ Cell getCentroidCell(const Polygon& polygon) {
double area = 0;
double cx = 0, cy = 0;
const auto& ring = polygon.outer();
const Point& origin = ring.at(0);
const double ox = origin.get<0>();
const double oy = origin.get<1>();

for (std::size_t i = 0, len = ring.size(), j = len - 1; i < len; j = i++) {
const Point& a = ring[i];
const Point& b = ring[j];
auto f = a.get<0>() * b.get<1>() - b.get<0>() * a.get<1>();
cx += (a.get<0>() + b.get<0>()) * f;
cy += (a.get<1>() + b.get<1>()) * f;
const double ax = a.get<0>() - ox;
const double ay = a.get<1>() - oy;
const double bx = b.get<0>() - ox;
const double by = b.get<1>() - oy;
auto f = ax * by - bx * ay;
cx += (ax + bx) * f;
cy += (ay + by) * f;
area += f * 3;
}

Point c { cx, cy };
return Cell(area == 0 ? ring.at(0) : Point { cx / area, cy / area }, 0, polygon);
return Cell(area == 0 ? ring.at(0) : Point { ox + cx / area, oy + cy / area }, 0, polygon);
}

} // namespace detail
Expand All @@ -144,7 +150,11 @@ Point polylabel(const Polygon& polygon, double precision = 0.00001, bool debug =

// a priority queue of cells in order of their "potential" (max distance to polygon)
auto compareMax = [] (const Cell& a, const Cell& b) {
return a.max < b.max;
if (a.max != b.max) return a.max < b.max;
if (a.d != b.d) return a.d < b.d;
if (a.h != b.h) return a.h > b.h;
if (a.c.get<0>() != b.c.get<0>()) return a.c.get<0>() > b.c.get<0>();
return a.c.get<1>() > b.c.get<1>();
};
using Queue = std::priority_queue<Cell, std::vector<Cell>, decltype(compareMax)>;
Queue cellQueue(compareMax);
Expand Down