wbprojection 0.1.0

Whitebox Projections is a map projection library for Rust, inspired by PROJ
Documentation 
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145

//! Geostationary Satellite View projection.
//!
//! This is a spherical geostationary projection suitable for typical
//! weather-satellite style navigation products. The implementation supports
//! both sweep-axis conventions used in practice:
//! - `sweep_x = true`  (GOES-style)
//! - `sweep_x = false` (Meteosat-style)

use super::{ProjectionImpl, ProjectionParams};
use crate::error::{ProjectionError, Result};
use crate::{to_degrees, to_radians};

pub(super) struct GeostationaryProj {
    a: f64,
    lon0: f64,
    fe: f64,
    fn_: f64,
    sweep_x: bool,
    h_total: f64,
}

impl GeostationaryProj {
    pub fn new(p: &ProjectionParams, satellite_height: f64, sweep_x: bool) -> Result<Self> {
        if satellite_height <= 0.0 {
            return Err(ProjectionError::invalid_param(
                "satellite_height",
                "must be positive",
            ));
        }

        let a = p.ellipsoid.a;
        Ok(Self {
            a,
            lon0: to_radians(p.lon0),
            fe: p.false_easting,
            fn_: p.false_northing,
            sweep_x,
            h_total: a + satellite_height,
        })
    }
}

impl ProjectionImpl for GeostationaryProj {
    fn forward(&self, lon_deg: f64, lat_deg: f64) -> Result<(f64, f64)> {
        let lon = to_radians(lon_deg);
        let lat = to_radians(lat_deg);
        let lam = lon - self.lon0;

        let cos_lat = lat.cos();
        let sin_lat = lat.sin();
        let cos_lam = lam.cos();
        let sin_lam = lam.sin();

        let r1 = self.h_total - self.a * cos_lat * cos_lam;
        let r2 = self.a * cos_lat * sin_lam;
        let r3 = self.a * sin_lat;

        // Visible hemisphere test from satellite viewpoint.
        if self.h_total * (self.h_total - self.a * cos_lat * cos_lam) < r2 * r2 + r3 * r3 {
            return Err(ProjectionError::out_of_bounds(
                "point is outside geostationary visible hemisphere",
            ));
        }

        let (x_ang, y_ang) = if self.sweep_x {
            (r2.atan2(r1), r3.atan2((r1 * r1 + r2 * r2).sqrt()))
        } else {
            (r2.atan2((r1 * r1 + r3 * r3).sqrt()), r3.atan2(r1))
        };

        Ok((self.a * x_ang + self.fe, self.a * y_ang + self.fn_))
    }

    fn inverse(&self, x: f64, y: f64) -> Result<(f64, f64)> {
        let x_ang = (x - self.fe) / self.a;
        let y_ang = (y - self.fn_) / self.a;

        let tx = x_ang.tan();
        let ty = y_ang.tan();

        let c = (1.0 + tx * tx) * (1.0 + ty * ty);
        let disc = self.h_total * self.h_total - c * (self.h_total * self.h_total - self.a * self.a);
        if disc < 0.0 {
            return Err(ProjectionError::out_of_bounds(
                "projected point is outside geostationary domain",
            ));
        }

        let r1 = (self.h_total - disc.sqrt()) / c;

        let (r2, r3) = if self.sweep_x {
            (r1 * tx, r1 * (1.0 + tx * tx).sqrt() * ty)
        } else {
            (r1 * (1.0 + ty * ty).sqrt() * tx, r1 * ty)
        };

        let xg = self.h_total - r1;
        let yg = r2;
        let zg = r3;

        let lon = self.lon0 + yg.atan2(xg);
        let lat = zg.atan2((xg * xg + yg * yg).sqrt());

        Ok((to_degrees(lon), to_degrees(lat)))
    }
}

#[cfg(test)]
mod tests {
    use crate::projections::{Projection, ProjectionKind, ProjectionParams};

    #[test]
    fn round_trip_geos_sweep_x() {
        let proj = Projection::new(
            ProjectionParams::new(ProjectionKind::Geostationary {
                satellite_height: 35_786_023.0,
                sweep_x: true,
            })
            .with_lon0(-75.0),
        )
        .unwrap();

        let (x, y) = proj.forward(-80.0, 20.0).unwrap();
        let (lon, lat) = proj.inverse(x, y).unwrap();
        assert!((lon + 80.0).abs() < 1e-6);
        assert!((lat - 20.0).abs() < 1e-6);
    }

    #[test]
    fn round_trip_geos_sweep_y() {
        let proj = Projection::new(
            ProjectionParams::new(ProjectionKind::Geostationary {
                satellite_height: 35_786_023.0,
                sweep_x: false,
            })
            .with_lon0(0.0),
        )
        .unwrap();

        let (x, y) = proj.forward(5.0, 15.0).unwrap();
        let (lon, lat) = proj.inverse(x, y).unwrap();
        assert!((lon - 5.0).abs() < 1e-6);
        assert!((lat - 15.0).abs() < 1e-6);
    }
}