squarepeg 0.4.0

A library for partitioning the Earth's geography
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
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236

// mapgrid.rs
//
// Copyright (c) 2019-2026  Douglas Lau
//
use crate::geo::WebMercatorPos;
use crate::peg::Peg;
use pointy::{BBox, Pt, Transform};

/// A grid used to address [Peg]s on a map
///
/// The grid has an associated [spatial reference ID], which should use
/// projected coordinates.  Use `default()` for [Web Mercator].
///
/// [Peg]: struct.Peg.html
/// [Spatial reference ID]: https://en.wikipedia.org/wiki/Spatial_reference_system
/// [Web Mercator]: https://en.wikipedia.org/wiki/Web_Mercator_projection
#[derive(Clone, Debug)]
pub struct MapGrid {
    /// Spatial reference ID
    srid: i32,

    /// Bounding box
    bbox: BBox<f64>,
}

impl Default for MapGrid {
    fn default() -> Self {
        const WEB_MERCATOR_SRID: i32 = 3857;
        let srid = WEB_MERCATOR_SRID;
        let bbox = WebMercatorPos::bbox();
        Self { srid, bbox }
    }
}

impl MapGrid {
    /// Create a new map grid
    ///
    /// * `srid` Spatial reference ID
    /// * `bbox` Bounding box
    pub fn new(srid: i32, bbox: BBox<f64>) -> Self {
        MapGrid { srid, bbox }
    }

    /// Get the spatial reference ID
    pub fn srid(&self) -> i32 {
        self.srid
    }

    /// Get the bounding box of the map grid
    pub fn bbox(&self) -> BBox<f64> {
        self.bbox
    }

    /// Get the bounding box of a Peg
    pub fn peg_bbox(&self, peg: Peg) -> BBox<f64> {
        let px = self.bbox.x_min(); // west edge
        let py = self.bbox.y_max(); // north edge
        let pz = zoom_scale(peg.z());
        let sx = self.bbox.x_span() * pz;
        let sy = self.bbox.y_span() * pz;
        let t = Transform::with_scale(sx, -sy).translate(px, py);
        let pegx = f64::from(peg.x());
        let pegy = f64::from(peg.y());
        let p0 = t * Pt::new(pegx, pegy);
        let p1 = t * Pt::new(pegx + 1.0, pegy + 1.0);
        BBox::from((p0, p1))
    }

    /// Get transform to Peg coördinates (range 0 to 1)
    pub fn peg_transform(&self, peg: Peg) -> Transform<f64> {
        let px = self.bbox.x_min(); // west edge
        let py = self.bbox.y_max(); // north edge
        let pz = f64::from(1 << peg.z());
        let sx = pz / self.bbox.x_span();
        let sy = pz / self.bbox.y_span();
        let pegx = f64::from(peg.x());
        let pegy = f64::from(peg.y());
        Transform::with_translate(-px, -py)
            .scale(sx, -sy)
            .translate(-pegx, -pegy)
    }

    /// Get Peg for a position (zoom, x, y)
    pub fn zxy_peg(&self, zoom: u32, x: f64, y: f64) -> Option<Peg> {
        let peg = Peg::new(zoom, 0, 0)?;
        if x < self.bbox.x_min() || x > self.bbox.x_max() {
            return None;
        }
        if y < self.bbox.y_min() || y > self.bbox.y_max() {
            return None;
        }
        let pz = f64::from(1 << peg.z());
        let tx = -self.bbox.x_min();
        let ty = -self.bbox.y_min();
        let sx = pz / self.bbox.x_span();
        let sy = pz / self.bbox.y_span();
        let t = Transform::with_translate(tx, ty).scale(sx, sy);
        let pt = Pt::new(x, -y) * t;
        let x = pt.x.floor() as u32;
        let y = pt.y.floor() as u32;
        Peg::new(zoom, x, y)
    }
}

/// Calculate scales at one zoom level
fn zoom_scale(zoom: u32) -> f64 {
    1.0 / f64::from(1 << zoom)
}

#[cfg(test)]
mod test {
    use super::*;
    use crate::geo::*;

    #[test]
    fn test_peg_bbox() {
        let g = MapGrid::default();
        let peg = Peg::new(0, 0, 0).unwrap();
        let b = g.peg_bbox(peg);
        assert_eq!(b.x_min(), -20037508.3427892480);
        assert_eq!(b.x_max(), 20037508.3427892480);
        assert_eq!(b.y_min(), -20037508.3427892480);
        assert_eq!(b.y_max(), 20037508.3427892480);

        let peg = Peg::new(1, 0, 0).unwrap();
        let b = g.peg_bbox(peg);
        assert_eq!(b.x_min(), -20037508.3427892480);
        assert_eq!(b.x_max(), 0.0);
        assert_eq!(b.y_min(), 0.0);
        assert_eq!(b.y_max(), 20037508.3427892480);

        let peg = Peg::new(1, 1, 1).unwrap();
        let b = g.peg_bbox(peg);
        assert_eq!(b.x_min(), 0.0);
        assert_eq!(b.x_max(), 20037508.3427892480);
        assert_eq!(b.y_min(), -20037508.3427892480);
        assert_eq!(b.y_max(), 0.0);

        let peg = Peg::new(10, 246, 368).unwrap();
        let b = g.peg_bbox(peg);
        assert_eq!(b.x_min(), -10410111.756214727);
        assert_eq!(b.x_max(), -10370975.997732716);
        assert_eq!(b.y_min(), 5596413.462927466);
        assert_eq!(b.y_max(), 5635549.221409475);
    }

    #[test]
    fn test_peg_transform() {
        let g = MapGrid::default();
        let peg = Peg::new(0, 0, 0).unwrap();
        let t = g.peg_transform(peg);
        assert_eq!(
            Pt::new(0.0, 0.0),
            t * Pt::new(-20037508.3427892480, 20037508.3427892480)
        );
        assert_eq!(
            Pt::new(1.0, 1.0),
            t * Pt::new(20037508.3427892480, -20037508.3427892480)
        );

        let peg = Peg::new(1, 0, 0).unwrap();
        let t = g.peg_transform(peg);
        assert_eq!(
            Pt::new(0.0, 0.0),
            t * Pt::new(-20037508.3427892480, 20037508.3427892480)
        );
        assert_eq!(Pt::new(1.0, 1.0), t * Pt::new(0.0, 0.0));

        let peg = Peg::new(1, 1, 1).unwrap();
        let t = g.peg_transform(peg);
        assert_eq!(Pt::new(0.0, 0.0), t * Pt::new(0.0, 0.0));
        assert_eq!(
            Pt::new(1.0, 1.0),
            t * Pt::new(20037508.3427892480, -20037508.3427892480)
        );

        let peg = Peg::new(10, 246, 368).unwrap();
        let t = g.peg_transform(peg);
        assert_eq!(
            Pt::new(0.0, 0.0),
            t * Pt::new(-10410111.756214727, 5635549.221409475)
        );
        assert_eq!(
            Pt::new(1.0, 0.9999999999999716),
            t * Pt::new(-10370975.997732716, 5596413.462927466)
        );
    }

    #[test]
    fn test_invalid_peg() {
        let g = MapGrid::default();
        let mut pos: WebMercatorPos = Wgs84Pos::new(-180.0, 0.0).into();
        assert!(g.zxy_peg(0, pos.x - 1.0, pos.y).is_none());
        pos = Wgs84Pos::new(180.0, 0.0).into();
        assert!(g.zxy_peg(0, pos.x + 1.0, pos.y).is_none());
        pos = Wgs84Pos::new(0.0, -86.0).into();
        assert!(g.zxy_peg(0, pos.x, pos.y - 1.0).is_none());
        pos = Wgs84Pos::new(0.0, 86.0).into();
        assert!(g.zxy_peg(0, pos.x, pos.y + 1.0).is_none());
    }

    fn check_pos(pos: WebMercatorPos, peg: Peg) {
        let g = MapGrid::default();
        assert_eq!(peg, g.zxy_peg(peg.z(), pos.x, pos.y).unwrap());
    }

    #[test]
    fn test_find_peg() {
        let pos = Wgs84Pos::new(0.0, 0.0).into();
        check_pos(pos, Peg::new(0, 0, 0).unwrap());
        // Northwest corner (zoom 0)
        let pos = Wgs84Pos::new(-180.0, 85.051).into();
        check_pos(pos, Peg::new(0, 0, 0).unwrap());
        // Southeast corner (zoom 0)
        let pos = Wgs84Pos::new(180.0, -85.051).into();
        check_pos(pos, Peg::new(0, 0, 0).unwrap());
        // Northwest corner (zoom 1)
        let pos = Wgs84Pos::new(-180.0, 85.051).into();
        check_pos(pos, Peg::new(1, 0, 0).unwrap());
        // Near Center (zoom 1)
        let pos = Wgs84Pos::new(-0.0000001, 0.0000001).into();
        check_pos(pos, Peg::new(1, 0, 0).unwrap());
        // Center (zoom 1)
        let pos = Wgs84Pos::new(0.0, 0.0).into();
        check_pos(pos, Peg::new(1, 1, 1).unwrap());
        // Northeast corner (zoom 1)
        let pos = Wgs84Pos::new(180.0, 85.051).into();
        check_pos(pos, Peg::new(1, 1, 0).unwrap());
        // Southeast corner (zoom 1)
        let pos = Wgs84Pos::new(180.0, -85.051).into();
        check_pos(pos, Peg::new(1, 1, 1).unwrap());
        // Somewhere in Minnesota (zoom 10)
        let pos = Wgs84Pos::new(-93.5, 45.0).into();
        check_pos(pos, Peg::new(10, 246, 368).unwrap());
    }
}