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geo 0.9.1

Geospatial primitives and algorithms
Documentation 
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use num_traits::Float;
use ::{Bbox, Line, LineString, MultiPolygon, Polygon};

use algorithm::winding_order::twice_signed_ring_area;

/// Calculation of the area.

pub trait Area<T>
where
    T: Float,
{
    /// Area of polygon.
    /// See: https://en.wikipedia.org/wiki/Polygon
    ///
    /// ```
    /// use geo::{Coordinate, Point, LineString, Polygon};
    /// use geo::algorithm::area::Area;
    /// let p = |x, y| Point(Coordinate { x: x, y: y });
    /// let v = Vec::new();
    /// let linestring = LineString(vec![p(0., 0.), p(5., 0.), p(5., 6.), p(0., 6.), p(0., 0.)]);
    /// let poly = Polygon::new(linestring, v);
    /// assert_eq!(poly.area(), 30.);
    /// ```
    fn area(&self) -> T;
}

fn get_linestring_area<T>(linestring: &LineString<T>) -> T where T: Float {
    twice_signed_ring_area(linestring) / (T::one() + T::one())
}

impl<T> Area<T> for Line<T>
where
    T: Float,
{
    fn area(&self) -> T {
        T::zero()
    }
}

impl<T> Area<T> for Polygon<T>
where
    T: Float,
{
    fn area(&self) -> T {
        self.interiors
            .iter()
            .fold(get_linestring_area(&self.exterior), |total, next| {
                total - get_linestring_area(next)
            })
    }
}

impl<T> Area<T> for MultiPolygon<T>
where
    T: Float,
{
    fn area(&self) -> T {
        self.0
            .iter()
            .fold(T::zero(), |total, next| {
                total + next.area()
            })
    }
}

impl<T> Area<T> for Bbox<T>
where
    T: Float,
{
    fn area(&self) -> T {
        (self.xmax - self.xmin) * (self.ymax - self.ymin)
    }
}

#[cfg(test)]
mod test {
    use ::{Bbox, Coordinate, Line, LineString, MultiPolygon, Point, Polygon};
    use algorithm::area::Area;

    // Area of the polygon
    #[test]
    fn area_empty_polygon_test() {
        let poly = Polygon::<f64>::new(LineString(Vec::new()), Vec::new());
        assert_relative_eq!(poly.area(), 0.);
    }

    #[test]
    fn area_one_point_polygon_test() {
        let poly = Polygon::new(LineString(vec![Point::new(1., 0.)]), Vec::new());
        assert_relative_eq!(poly.area(), 0.);
    }
    #[test]
    fn area_polygon_test() {
        let p = |x, y| Point(Coordinate { x: x, y: y });
        let linestring = LineString(vec![p(0., 0.), p(5., 0.), p(5., 6.), p(0., 6.), p(0., 0.)]);
        let poly = Polygon::new(linestring, Vec::new());
        assert_relative_eq!(poly.area(), 30.);
    }
    #[test]
    fn bbox_test() {
        let bbox = Bbox {
            xmin: 10.,
            xmax: 20.,
            ymin: 30.,
            ymax: 40.,
        };
        assert_relative_eq!(bbox.area(), 100.);
    }
    #[test]
    fn area_polygon_inner_test() {
        let p = |x, y| Point(Coordinate { x: x, y: y });
        let outer = LineString(vec![
            p(0., 0.),
            p(10., 0.),
            p(10., 10.),
            p(0., 10.),
            p(0., 0.),
        ]);
        let inner0 = LineString(vec![p(1., 1.), p(2., 1.), p(2., 2.), p(1., 2.), p(1., 1.)]);
        let inner1 = LineString(vec![p(5., 5.), p(6., 5.), p(6., 6.), p(5., 6.), p(5., 5.)]);
        let poly = Polygon::new(outer, vec![inner0, inner1]);
        assert_relative_eq!(poly.area(), 98.);
    }
    #[test]
    fn area_multipolygon_test() {
        let p = |x, y| Point(Coordinate { x: x, y: y });
        let poly0 = Polygon::new(
            LineString(vec![
                p(0., 0.),
                p(10., 0.),
                p(10., 10.),
                p(0., 10.),
                p(0., 0.),
            ]),
            Vec::new(),
        );
        let poly1 = Polygon::new(
            LineString(vec![p(1., 1.), p(2., 1.), p(2., 2.), p(1., 2.), p(1., 1.)]),
            Vec::new(),
        );
        let poly2 = Polygon::new(
            LineString(vec![p(5., 5.), p(6., 5.), p(6., 6.), p(5., 6.), p(5., 5.)]),
            Vec::new(),
        );
        let mpoly = MultiPolygon(vec![poly0, poly1, poly2]);
        assert_eq!(mpoly.area(), 102.);
        assert_relative_eq!(mpoly.area(), 102.);
    }
    #[test]
    fn area_line_test() {
        let p = |x, y| Point(Coordinate { x: x, y: y });
        let line1 = Line::new(p(0.0, 0.0), p(1.0, 1.0));
        assert_eq!(line1.area(), 0.);
    }
}