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Implements Ramer-Douglas-Peucker simplification algorithm (TheAlgorit…
…hms#710) * Implements Ramer-Douglas-Peucker simplification algorithm * Apply requested changes * Cargo format * Cargo clippy * Apply requested changes * style: use slice --------- Co-authored-by: Piotr Idzik <65706193+vil02@users.noreply.github.com>
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use crate::geometry::Point; | ||
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pub fn ramer_douglas_peucker(points: &[Point], epsilon: f64) -> Vec<Point> { | ||
if points.len() < 3 { | ||
return points.to_vec(); | ||
} | ||
let mut dmax = 0.0; | ||
let mut index = 0; | ||
let end = points.len() - 1; | ||
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for i in 1..end { | ||
let d = perpendicular_distance(&points[i], &points[0], &points[end]); | ||
if d > dmax { | ||
index = i; | ||
dmax = d; | ||
} | ||
} | ||
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if dmax > epsilon { | ||
let mut results = ramer_douglas_peucker(&points[..=index], epsilon); | ||
results.pop(); | ||
results.extend(ramer_douglas_peucker(&points[index..], epsilon)); | ||
results | ||
} else { | ||
vec![points[0].clone(), points[end].clone()] | ||
} | ||
} | ||
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fn perpendicular_distance(p: &Point, a: &Point, b: &Point) -> f64 { | ||
let num = (b.y - a.y) * p.x - (b.x - a.x) * p.y + b.x * a.y - b.y * a.x; | ||
let den = a.euclidean_distance(b); | ||
num.abs() / den | ||
} | ||
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#[cfg(test)] | ||
mod tests { | ||
use super::*; | ||
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macro_rules! test_perpendicular_distance { | ||
($($name:ident: $test_case:expr,)*) => { | ||
$( | ||
#[test] | ||
fn $name() { | ||
let (p, a, b, expected) = $test_case; | ||
assert_eq!(perpendicular_distance(&p, &a, &b), expected); | ||
assert_eq!(perpendicular_distance(&p, &b, &a), expected); | ||
} | ||
)* | ||
}; | ||
} | ||
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test_perpendicular_distance! { | ||
basic: (Point::new(4.0, 0.0), Point::new(0.0, 0.0), Point::new(0.0, 3.0), 4.0), | ||
basic_shifted_1: (Point::new(4.0, 1.0), Point::new(0.0, 1.0), Point::new(0.0, 4.0), 4.0), | ||
basic_shifted_2: (Point::new(2.0, 1.0), Point::new(-2.0, 1.0), Point::new(-2.0, 4.0), 4.0), | ||
} | ||
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#[test] | ||
fn test_ramer_douglas_peucker_polygon() { | ||
let a = Point::new(0.0, 0.0); | ||
let b = Point::new(1.0, 0.0); | ||
let c = Point::new(2.0, 0.0); | ||
let d = Point::new(2.0, 1.0); | ||
let e = Point::new(2.0, 2.0); | ||
let f = Point::new(1.0, 2.0); | ||
let g = Point::new(0.0, 2.0); | ||
let h = Point::new(0.0, 1.0); | ||
let polygon = vec![ | ||
a.clone(), | ||
b, | ||
c.clone(), | ||
d, | ||
e.clone(), | ||
f, | ||
g.clone(), | ||
h.clone(), | ||
]; | ||
let epsilon = 0.7; | ||
let result = ramer_douglas_peucker(&polygon, epsilon); | ||
assert_eq!(result, vec![a, c, e, g, h]); | ||
} | ||
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#[test] | ||
fn test_ramer_douglas_peucker_polygonal_chain() { | ||
let a = Point::new(0., 0.); | ||
let b = Point::new(2., 0.5); | ||
let c = Point::new(3., 3.); | ||
let d = Point::new(6., 3.); | ||
let e = Point::new(8., 4.); | ||
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let points = vec![a.clone(), b, c, d, e.clone()]; | ||
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let epsilon = 3.; // The epsilon is quite large, so the result will be a single line | ||
let result = ramer_douglas_peucker(&points, epsilon); | ||
assert_eq!(result, vec![a, e]); | ||
} | ||
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#[test] | ||
fn test_less_than_three_points() { | ||
let a = Point::new(0., 0.); | ||
let b = Point::new(1., 1.); | ||
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let epsilon = 0.1; | ||
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assert_eq!(ramer_douglas_peucker(&[], epsilon), vec![]); | ||
assert_eq!( | ||
ramer_douglas_peucker(&[a.clone()], epsilon), | ||
vec![a.clone()] | ||
); | ||
assert_eq!( | ||
ramer_douglas_peucker(&[a.clone(), b.clone()], epsilon), | ||
vec![a, b] | ||
); | ||
} | ||
} |