@gisatcz/ptr-tile-grid

ptr-tile-grid

Tile grid for globe.

Tile grid covers the whole globe. Extent of grid is [bottomLeft, topRight] [[-180,-90], [180, 90]].

It is possible to generate all tiles for a certain level. Zero lavel has two tiles. Tiles count rise quadratic with each level.

Function getGridForLevelAndExtent(level, extent) creates grid for asked level and extent. Extent parameter is optional and use whole globe as default.

import {getSizeForLevel} from './src/grid';

const grid0 = getGridForLevelAndExtent(0);
//[
//    [[-180,-90], [0,-90]]
//]
const grid1 = getGridForLevelAndExtent(1);
//[
//    [[-180,0], [-90,0], [0,0], [90,0]],
//    [[-180,-90], [-90,-90], [0,-90], [90,-90]]
//]
const grid2 = getGridForLevelAndExtent(2);
//[
//    [[-180,45], [-135,45], [-90,45], [-45,45], [0,45], [45,45], [90,45], [135,45]],
//    [[-180,0], [-135,0], [-90,0], [-45,0], [0,0], [45,0], [90,0], [135,0]],
//    [[-180,-45], [-135,-45], [-90,-45], [-45,-45], [0,-45], [45,-45], [90,-45], [135,-45]],
//    [[-180,-90], [-135,-90], [-90,-90], [-45,-90], [0,-90], [45,-90], [90,-90], [135,-90]]
// ]

Tiles for extent

import {getSizeForLevel} from './src/grid';

const grid2 = utils.getGridForLevelAndExtent(2, [
	[-10, -10],
	[10, 10],
]);
// [
//   [[-45,0], [0,0]],
//   [[-45,-45], [0,-45]
// ]

Tile

Tile is spherical square with same side size in degrees. Side size is same for all tiles in same level. Each tile is defined by left bottom (south west) corner longitude latitude.

import {getSizeForLevel} from './src/grid';

const level0 = getSizeForLevel(0); //180
const level1 = getSizeForLevel(1); //90
const level2 = getSizeForLevel(2); //45
const level3 = getSizeForLevel(3); //22.5
const level4 = getSizeForLevel(4); //11.25
const level5 = getSizeForLevel(5); //5.625
const level6 = getSizeForLevel(6); //2.8125
const level7 = getSizeForLevel(7); //1.40625
const level8 = getSizeForLevel(8); //0.703125
const level9 = getSizeForLevel(9); //0.3515625
const level10 = getSizeForLevel(10); //0.17578125

Level

Tile set is defined by pyramid of levels, where each next level has quadratically more tile than level before.

Base level is level 0 with two tiles and side size 180°.

Level is required parameter for function getGridForLevelAndExtent. Usual usecase how determinate right level is by getLevelByViewport(boxRange, viewportRange) , where boxrange is smaller size of visible map in meters and viewportRange is smaller size of viewport in pixels.

import {getLevelByViewport} from './src/grid';

const boxRange = 240; //meters
const viewport = 240; //pixels

const level0 = grid.getLevelByViewport(boxRange, viewport);
// level0 = 17

const level1 = grid.getLevelByViewport(50000000, 250);
// level1 = 0