geo 0.9.1

Geospatial primitives and algorithms
Documentation 
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use num_traits::Float;
use ::{LineString, MultiLineString, MultiPolygon, Point, Polygon};
use algorithm::euclidean_distance::EuclideanDistance;

// perpendicular distance from a point to a line
fn point_line_distance<T>(point: &Point<T>, start: &Point<T>, end: &Point<T>) -> T
where
    T: Float,
{
    if start == end {
        point.euclidean_distance(start)
    } else {
        let numerator = ((end.x() - start.x()) * (start.y() - point.y())
            - (start.x() - point.x()) * (end.y() - start.y()))
            .abs();
        let denominator = start.euclidean_distance(end);
        numerator / denominator
    }
}

// Ramer–Douglas-Peucker line simplification algorithm
fn rdp<T>(points: &[Point<T>], epsilon: &T) -> Vec<Point<T>>
where
    T: Float,
{
    if points.is_empty() {
        return points.to_vec();
    }
    let mut dmax = T::zero();
    let mut index: usize = 0;
    let mut distance: T;

    for (i, _) in points.iter().enumerate().take(points.len() - 1).skip(1) {
        distance = point_line_distance(&points[i], &points[0], &*points.last().unwrap());
        if distance > dmax {
            index = i;
            dmax = distance;
        }
    }
    if dmax > *epsilon {
        let mut intermediate = rdp(&points[..index + 1], &*epsilon);
        intermediate.pop();
        intermediate.extend_from_slice(&rdp(&points[index..], &*epsilon));
        intermediate
    } else {
        vec![*points.first().unwrap(), *points.last().unwrap()]
    }
}

/// Simplifies a geometry.
///
/// The [Ramer–Douglas–Peucker
/// algorithm](https://en.wikipedia.org/wiki/Ramer–Douglas–Peucker_algorithm) simplifes a
/// linestring. Polygons are simplified by running the RDP algorithm on all their constituent
/// rings. This may result in invalid Polygons, and has no guarantee of preserving topology.
///
/// Multi* objects are simplified by simplifing all their constituent geometries individually.
pub trait Simplify<T, Epsilon = T> {
    /// Returns the simplified representation of a geometry, using the [Ramer–Douglas–Peucker](https://en.wikipedia.org/wiki/Ramer–Douglas–Peucker_algorithm) algorithm
    ///
    /// ```
    /// use geo::{Point, LineString};
    /// use geo::algorithm::simplify::{Simplify};
    ///
    /// let mut vec = Vec::new();
    /// vec.push(Point::new(0.0, 0.0));
    /// vec.push(Point::new(5.0, 4.0));
    /// vec.push(Point::new(11.0, 5.5));
    /// vec.push(Point::new(17.3, 3.2));
    /// vec.push(Point::new(27.8, 0.1));
    /// let linestring = LineString(vec);
    /// let mut compare = Vec::new();
    /// compare.push(Point::new(0.0, 0.0));
    /// compare.push(Point::new(5.0, 4.0));
    /// compare.push(Point::new(11.0, 5.5));
    /// compare.push(Point::new(27.8, 0.1));
    /// let ls_compare = LineString(compare);
    /// let simplified = linestring.simplify(&1.0);
    /// assert_eq!(simplified, ls_compare)
    /// ```
    fn simplify(&self, epsilon: &T) -> Self
    where
        T: Float;
}

impl<T> Simplify<T> for LineString<T>
where
    T: Float,
{
    fn simplify(&self, epsilon: &T) -> LineString<T> {
        LineString(rdp(&self.0, epsilon))
    }
}

impl<T> Simplify<T> for MultiLineString<T>
where
    T: Float,
{
    fn simplify(&self, epsilon: &T) -> MultiLineString<T> {
        MultiLineString(self.0.iter().map(|l| l.simplify(epsilon)).collect())
    }
}

impl<T> Simplify<T> for Polygon<T>
where
    T: Float,
{
    fn simplify(&self, epsilon: &T) -> Polygon<T> {
        Polygon::new(
            self.exterior.simplify(epsilon),
            self.interiors.iter().map(|l| l.simplify(epsilon)).collect(),
        )
    }
}

impl<T> Simplify<T> for MultiPolygon<T>
where
    T: Float,
{
    fn simplify(&self, epsilon: &T) -> MultiPolygon<T> {
        MultiPolygon(self.0.iter().map(|p| p.simplify(epsilon)).collect())
    }
}

#[cfg(test)]
mod test {
    use ::{LineString, MultiLineString, MultiPolygon, Point, Polygon};
    use super::{point_line_distance, rdp, Simplify};

    #[test]
    fn perpdistance_test() {
        let start = Point::new(1.0, 2.0);
        let end = Point::new(3.0, 4.0);
        let p = Point::new(1.0, 1.0);
        let dist = point_line_distance(&p, &start, &end);
        assert_relative_eq!(dist, 0.7071067811865475);
    }
    #[test]
    fn rdp_test() {
        let mut vec = Vec::new();
        vec.push(Point::new(0.0, 0.0));
        vec.push(Point::new(5.0, 4.0));
        vec.push(Point::new(11.0, 5.5));
        vec.push(Point::new(17.3, 3.2));
        vec.push(Point::new(27.8, 0.1));
        let mut compare = Vec::new();
        compare.push(Point::new(0.0, 0.0));
        compare.push(Point::new(5.0, 4.0));
        compare.push(Point::new(11.0, 5.5));
        compare.push(Point::new(27.8, 0.1));
        let simplified = rdp(&vec, &1.0);
        assert_eq!(simplified, compare);
    }
    #[test]
    fn rdp_test_empty_linestring() {
        let vec = Vec::new();
        let compare = Vec::new();
        let simplified = rdp(&vec, &1.0);
        assert_eq!(simplified, compare);
    }
    #[test]
    fn rdp_test_two_point_linestring() {
        let mut vec = Vec::new();
        vec.push(Point::new(0.0, 0.0));
        vec.push(Point::new(27.8, 0.1));
        let mut compare = Vec::new();
        compare.push(Point::new(0.0, 0.0));
        compare.push(Point::new(27.8, 0.1));
        let simplified = rdp(&vec, &1.0);
        assert_eq!(simplified, compare);
    }

    #[test]
    fn multilinestring() {
        let mline = MultiLineString(vec![
            LineString(vec![
                Point::new(0.0, 0.0),
                Point::new(5.0, 4.0),
                Point::new(11.0, 5.5),
                Point::new(17.3, 3.2),
                Point::new(27.8, 0.1),
            ]),
        ]);

        let mline2 = mline.simplify(&1.0);

        assert_eq!(
            mline2,
            MultiLineString(vec![
                LineString(vec![
                    Point::new(0.0, 0.0),
                    Point::new(5.0, 4.0),
                    Point::new(11.0, 5.5),
                    Point::new(27.8, 0.1),
                ]),
            ])
        );
    }

    #[test]
    fn polygon() {
        let poly = Polygon::new(
            LineString(vec![
                Point::new(0., 0.),
                Point::new(0., 10.),
                Point::new(5., 11.),
                Point::new(10., 10.),
                Point::new(10., 0.),
                Point::new(0., 0.),
            ]),
            vec![],
        );

        let poly2 = poly.simplify(&2.);

        assert_eq!(
            poly2,
            Polygon::new(
                LineString(vec![
                    Point::new(0., 0.),
                    Point::new(0., 10.),
                    Point::new(10., 10.),
                    Point::new(10., 0.),
                    Point::new(0., 0.),
                ]),
                vec![]
            )
        );
    }

    #[test]
    fn multipolygon() {
        let mpoly = MultiPolygon(vec![
            Polygon::new(
                LineString(vec![
                    Point::new(0., 0.),
                    Point::new(0., 10.),
                    Point::new(5., 11.),
                    Point::new(10., 10.),
                    Point::new(10., 0.),
                    Point::new(0., 0.),
                ]),
                vec![],
            ),
        ]);

        let mpoly2 = mpoly.simplify(&2.);

        assert_eq!(
            mpoly2,
            MultiPolygon(vec![
                Polygon::new(
                    LineString(vec![
                        Point::new(0., 0.),
                        Point::new(0., 10.),
                        Point::new(10., 10.),
                        Point::new(10., 0.),
                        Point::new(0., 0.),
                    ]),
                    vec![],
                ),
            ])
        );
    }
}