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#[derive(Debug, PartialEq)]
pub struct Extent {
pub minx: f64,
pub miny: f64,
pub maxx: f64,
pub maxy: f64,
}
/// Min and max grid cell numbers
#[derive(Debug, PartialEq)]
pub struct ExtentInt {
pub minx: u32,
pub miny: u32,
pub maxx: u32,
pub maxy: u32,
}
#[derive(Debug, PartialEq)]
pub enum Origin {
TopLeft,
BottomLeft, // TopRight, BottomRight
}
#[derive(Debug, PartialEq)]
pub enum Unit {
M,
DD,
Ft,
}
// Credits: MapCache by Thomas Bonfort (http://mapserver.org/mapcache/)
#[derive(Debug)]
pub struct Grid {
/// The width and height of an individual tile, in pixels.
width: u16,
height: u16,
/// The geographical extent covered by the grid, in ground units (e.g. meters, degrees, feet, etc.).
/// Must be specified as 4 floating point numbers ordered as minx, miny, maxx, maxy.
/// The (minx,miny) point defines the origin of the grid, i.e. the pixel at the bottom left of the
/// bottom-left most tile is always placed on the (minx,miny) geographical point.
/// The (maxx,maxy) point is used to determine how many tiles there are for each zoom level.
pub extent: Extent,
/// Spatial reference system (PostGIS SRID).
pub srid: i32,
/// Grid units
pub units: Unit,
/// This is a list of resolutions for each of the zoom levels defined by the grid.
/// This must be supplied as a list of positive floating point values, ordered from largest to smallest.
/// The largest value will correspond to the grid’s zoom level 0. Resolutions
/// are expressed in “units-per-pixel”,
/// depending on the unit used by the grid (e.g. resolutions are in meters per
/// pixel for most grids used in webmapping).
resolutions: Vec<f64>,
/// Grid origin
pub origin: Origin,
/// Whether y tiles go from South->North (normal) or North->South (reversed)
pub reverse_y: bool,
}
impl Grid {
/// WGS84 grid
pub fn wgs84() -> Grid {
Grid {
width: 256,
height: 256,
extent: Extent {
minx: -180.0,
miny: -90.0,
maxx: 180.0,
maxy: 90.0,
},
srid: 4326,
units: Unit::DD,
resolutions: vec![0.703125000000000,
0.351562500000000,
0.175781250000000,
8.78906250000000e-2,
4.39453125000000e-2,
2.19726562500000e-2,
1.09863281250000e-2,
5.49316406250000e-3,
2.74658203125000e-3,
1.37329101562500e-3,
6.86645507812500e-4,
3.43322753906250e-4,
1.71661376953125e-4,
8.58306884765625e-5,
4.29153442382812e-5,
2.14576721191406e-5,
1.07288360595703e-5,
5.36441802978516e-6],
origin: Origin::BottomLeft,
reverse_y: false,
}
}
/// Web Mercator grid (Google maps compatible)
pub fn web_mercator() -> Grid {
Grid {
width: 256,
height: 256,
extent: Extent {
minx: -20037508.3427892480,
miny: -20037508.3427892480,
maxx: 20037508.3427892480,
maxy: 20037508.3427892480,
},
srid: 3857,
units: Unit::M,
resolutions: vec![156543.0339280410,
78271.51696402048,
39135.75848201023,
19567.87924100512,
9783.939620502561,
4891.969810251280,
2445.984905125640,
1222.992452562820,
611.4962262814100,
305.7481131407048,
152.8740565703525,
76.43702828517624,
38.21851414258813,
19.10925707129406,
9.554628535647032,
4.777314267823516,
2.388657133911758,
1.194328566955879,
0.5971642834779395,
0.2985821417389700,
0.1492910708694850,
0.0746455354347424,
0.0373227677173712],
origin: Origin::BottomLeft,
reverse_y: true,
}
}
pub fn nlevels(&self) -> u8 {
self.resolutions.len() as u8
}
pub fn maxzoom(&self) -> u8 {
self.nlevels() - 1
}
pub fn pixel_width(&self, zoom: u8) -> f64 {
self.resolutions[zoom as usize] //TODO: assumes grid unit 'm'
}
pub fn scale_denominator(&self, zoom: u8) -> f64 {
let pixel_screen_width = 0.0254 / 96.0; //FIXME: assumes 96dpi - check with mapnik
self.pixel_width(zoom) / pixel_screen_width
}
/// Extent of a given tile in the grid given its x, y, and z in TMS adressing scheme
pub fn tile_extent(&self, z: u8, x: u32, y: u32) -> Extent {
let zoom = z;
let xtile = x;
let ytile = if self.reverse_y {
let res = self.resolutions[zoom as usize];
let unitheight = self.height as f64 * res;
let maxy = ((self.extent.maxy - self.extent.minx - 0.01 * unitheight) / unitheight)
.ceil() as u32;
maxy.saturating_sub(y).saturating_sub(1)
} else {
y
};
// based on mapcache_grid_get_tile_extent
let res = self.resolutions[zoom as usize];
let tile_sx = self.width as f64;
let tile_sy = self.height as f64;
match self.origin {
Origin::BottomLeft => {
Extent {
minx: self.extent.minx + (res * xtile as f64 * tile_sx),
miny: self.extent.miny + (res * ytile as f64 * tile_sy),
maxx: self.extent.minx + (res * (xtile + 1) as f64 * tile_sx),
maxy: self.extent.miny + (res * (ytile + 1) as f64 * tile_sy),
}
}
Origin::TopLeft => {
Extent {
minx: self.extent.minx + (res * xtile as f64 * tile_sx),
miny: self.extent.maxy - (res * (ytile + 1) as f64 * tile_sy),
maxx: self.extent.minx + (res * (xtile + 1) as f64 * tile_sx),
maxy: self.extent.maxy - (res * ytile as f64 * tile_sy),
}
}
}
}
/// (maxx, maxy) of grid level
pub fn level_limit(&self, zoom: u8) -> (u32, u32) {
let res = self.resolutions[zoom as usize];
let unitheight = self.height as f64 * res;
let unitwidth = self.width as f64 * res;
let maxy = ((self.extent.maxy - self.extent.miny - 0.01 * unitheight) / unitheight)
.ceil() as u32;
let maxx = ((self.extent.maxx - self.extent.miny - 0.01 * unitwidth) / unitwidth)
.ceil() as u32;
(maxx, maxy)
}
/// Tile index limits covering extent
pub fn tile_limits(&self, extent: Extent, tolerance: i32) -> Vec<ExtentInt> {
// Based on mapcache_grid_compute_limits
const EPSILON: f64 = 0.0000001;
let nlevels = self.resolutions.len() as u8;
(0..nlevels)
.map(|i| {
let res = self.resolutions[i as usize];
let unitheight = self.height as f64 * res;
let unitwidth = self.width as f64 * res;
let (level_maxx, level_maxy) = self.level_limit(i);
let (mut minx, mut maxx, mut miny, mut maxy) =
match self.origin {
Origin::BottomLeft => {
((((extent.minx - self.extent.minx) / unitwidth + EPSILON)
.floor() as i32) - tolerance,
(((extent.maxx - self.extent.minx) / unitwidth - EPSILON)
.ceil() as i32) + tolerance,
(((extent.miny - self.extent.miny) / unitheight + EPSILON)
.floor() as i32) - tolerance,
(((extent.maxy - self.extent.miny) / unitheight - EPSILON)
.ceil() as i32) + tolerance)
}
Origin::TopLeft => {
((((extent.minx - self.extent.minx) / unitwidth + EPSILON)
.floor() as i32) - tolerance,
(((extent.maxx - self.extent.minx) / unitwidth - EPSILON)
.ceil() as i32) + tolerance,
(((self.extent.maxy - extent.maxy) / unitheight + EPSILON)
.floor() as i32) - tolerance,
(((self.extent.maxy - extent.miny) / unitheight - EPSILON)
.ceil() as i32) + tolerance)
}
};
// to avoid requesting out-of-range tiles
if minx < 0 {
minx = 0;
}
if maxx > level_maxx as i32 {
maxx = level_maxx as i32
};
if miny < 0 {
miny = 0
};
if maxy > level_maxy as i32 {
maxy = level_maxy as i32
};
ExtentInt {
minx: minx as u32,
maxx: maxx as u32,
miny: miny as u32,
maxy: maxy as u32,
}
})
.collect()
}
}