Polylabel-rs

A Rust implementation of the Polylabel algorithm

The orange dot is the polygon centroid. The teal dot is the ideal label position. Red boxes show the search space.

You can generate this visualisation yourself by cloning this repo, switching to the visualise branch, and opening the visualise.ipynb Jupyter notebook, then stepping through the cells. You can also easily visualise a Polygon of your own using the notebook.

How to Use

extern crate polylabel;
use polylabel::polylabel;

extern crate geo;
use geo::{Point, LineString, Polygon};

let coords = vec![
    (0.0, 0.0),
    (4.0, 0.0),
    (4.0, 1.0),
    (1.0, 1.0),
    (1.0, 4.0),
    (0.0, 4.0),
    (0.0, 0.0)
];
let poly = Polygon::new(coords.into(), vec![]);
let label_pos = polylabel(&poly, &0.10);
// Point(0.5625, 0.5625)

Documentation

https://docs.rs/polylabel

FFI

Call polylabel_ffi with the following three mandatory arguments:

• Array (a struct with two fields):
  • data: a void pointer to an array of two-element c_doubles, the exterior Polygon shell)
  • len: the length of the data array, a size_t
• WrapperArray (a struct with two fields):
  • data: a void pointer to an array of Arrays, each entry representing and interior Polygon ring. Empty if there are no rings.
  • len: the length of the data array, a size_t. 0 if it's empty.
• tolerance, a c_double

The function returns a struct with two c_double fields:

• x_pos
• y_pos

A Python example is available in ffi.py

Performance

Finding a label position on a ~9k-vertex polygon using a tolerance of 10.0 takes around 5 ms on a 1.8 GHz Core i7 processor. Higher tolerances will significantly increase this time; finding a position on the same polygon using a tolerance of 1.0 takes around 80 ms, though in general this level of precision isn't required.

Binaries

Binary libs for:

• x86_64 *nix (built using manylinux1, thus easy to include in Python 2.7 / 3.5 / 3.6 wheels) and OS X
• i686 and x86_64 Windows

are available in releases.

License

MIT