geojson-vt
Version:
Slice GeoJSON data into vector tiles efficiently
890 lines (724 loc) • 28 kB
JavaScript
(function (global, factory) {
typeof exports === 'object' && typeof module !== 'undefined' ? module.exports = factory() :
typeof define === 'function' && define.amd ? define(factory) :
(global = typeof globalThis !== 'undefined' ? globalThis : global || self, global.geojsonvt = factory());
})(this, (function () { 'use strict';
// calculate simplification data using optimized Douglas-Peucker algorithm
function simplify(coords, first, last, sqTolerance) {
let maxSqDist = sqTolerance;
const mid = first + ((last - first) >> 1);
let minPosToMid = last - first;
let index;
const ax = coords[first];
const ay = coords[first + 1];
const bx = coords[last];
const by = coords[last + 1];
for (let i = first + 3; i < last; i += 3) {
const d = getSqSegDist(coords[i], coords[i + 1], ax, ay, bx, by);
if (d > maxSqDist) {
index = i;
maxSqDist = d;
} else if (d === maxSqDist) {
// a workaround to ensure we choose a pivot close to the middle of the list,
// reducing recursion depth, for certain degenerate inputs
// https://github.com/mapbox/geojson-vt/issues/104
const posToMid = Math.abs(i - mid);
if (posToMid < minPosToMid) {
index = i;
minPosToMid = posToMid;
}
}
}
if (maxSqDist > sqTolerance) {
if (index - first > 3) simplify(coords, first, index, sqTolerance);
coords[index + 2] = maxSqDist;
if (last - index > 3) simplify(coords, index, last, sqTolerance);
}
}
// square distance from a point to a segment
function getSqSegDist(px, py, x, y, bx, by) {
let dx = bx - x;
let dy = by - y;
if (dx !== 0 || dy !== 0) {
const t = ((px - x) * dx + (py - y) * dy) / (dx * dx + dy * dy);
if (t > 1) {
x = bx;
y = by;
} else if (t > 0) {
x += dx * t;
y += dy * t;
}
}
dx = px - x;
dy = py - y;
return dx * dx + dy * dy;
}
function createFeature(id, type, geom, tags) {
const feature = {
id: id == null ? null : id,
type,
geometry: geom,
tags,
minX: Infinity,
minY: Infinity,
maxX: -Infinity,
maxY: -Infinity
};
if (type === 'Point' || type === 'MultiPoint' || type === 'LineString') {
calcLineBBox(feature, geom);
} else if (type === 'Polygon') {
// the outer ring (ie [0]) contains all inner rings
calcLineBBox(feature, geom[0]);
} else if (type === 'MultiLineString') {
for (const line of geom) {
calcLineBBox(feature, line);
}
} else if (type === 'MultiPolygon') {
for (const polygon of geom) {
// the outer ring (ie [0]) contains all inner rings
calcLineBBox(feature, polygon[0]);
}
}
return feature;
}
function calcLineBBox(feature, geom) {
for (let i = 0; i < geom.length; i += 3) {
feature.minX = Math.min(feature.minX, geom[i]);
feature.minY = Math.min(feature.minY, geom[i + 1]);
feature.maxX = Math.max(feature.maxX, geom[i]);
feature.maxY = Math.max(feature.maxY, geom[i + 1]);
}
}
// converts GeoJSON feature into an intermediate projected JSON vector format with simplification data
function convert(data, options) {
const features = [];
if (data.type === 'FeatureCollection') {
for (let i = 0; i < data.features.length; i++) {
convertFeature(features, data.features[i], options, i);
}
} else if (data.type === 'Feature') {
convertFeature(features, data, options);
} else {
// single geometry or a geometry collection
convertFeature(features, {geometry: data}, options);
}
return features;
}
function convertFeature(features, geojson, options, index) {
if (!geojson.geometry) return;
const coords = geojson.geometry.coordinates;
if (coords && coords.length === 0) return;
const type = geojson.geometry.type;
const tolerance = Math.pow(options.tolerance / ((1 << options.maxZoom) * options.extent), 2);
let geometry = [];
let id = geojson.id;
if (options.promoteId) {
id = geojson.properties[options.promoteId];
} else if (options.generateId) {
id = index || 0;
}
if (type === 'Point') {
convertPoint(coords, geometry);
} else if (type === 'MultiPoint') {
for (const p of coords) {
convertPoint(p, geometry);
}
} else if (type === 'LineString') {
convertLine(coords, geometry, tolerance, false);
} else if (type === 'MultiLineString') {
if (options.lineMetrics) {
// explode into linestrings to be able to track metrics
for (const line of coords) {
geometry = [];
convertLine(line, geometry, tolerance, false);
features.push(createFeature(id, 'LineString', geometry, geojson.properties));
}
return;
} else {
convertLines(coords, geometry, tolerance, false);
}
} else if (type === 'Polygon') {
convertLines(coords, geometry, tolerance, true);
} else if (type === 'MultiPolygon') {
for (const polygon of coords) {
const newPolygon = [];
convertLines(polygon, newPolygon, tolerance, true);
geometry.push(newPolygon);
}
} else if (type === 'GeometryCollection') {
for (const singleGeometry of geojson.geometry.geometries) {
convertFeature(features, {
id,
geometry: singleGeometry,
properties: geojson.properties
}, options, index);
}
return;
} else {
throw new Error('Input data is not a valid GeoJSON object.');
}
features.push(createFeature(id, type, geometry, geojson.properties));
}
function convertPoint(coords, out) {
out.push(projectX(coords[0]), projectY(coords[1]), 0);
}
function convertLine(ring, out, tolerance, isPolygon) {
let x0, y0;
let size = 0;
for (let j = 0; j < ring.length; j++) {
const x = projectX(ring[j][0]);
const y = projectY(ring[j][1]);
out.push(x, y, 0);
if (j > 0) {
if (isPolygon) {
size += (x0 * y - x * y0) / 2; // area
} else {
size += Math.sqrt(Math.pow(x - x0, 2) + Math.pow(y - y0, 2)); // length
}
}
x0 = x;
y0 = y;
}
const last = out.length - 3;
out[2] = 1;
simplify(out, 0, last, tolerance);
out[last + 2] = 1;
out.size = Math.abs(size);
out.start = 0;
out.end = out.size;
}
function convertLines(rings, out, tolerance, isPolygon) {
for (let i = 0; i < rings.length; i++) {
const geom = [];
convertLine(rings[i], geom, tolerance, isPolygon);
out.push(geom);
}
}
function projectX(x) {
return x / 360 + 0.5;
}
function projectY(y) {
const sin = Math.sin(y * Math.PI / 180);
const y2 = 0.5 - 0.25 * Math.log((1 + sin) / (1 - sin)) / Math.PI;
return y2 < 0 ? 0 : y2 > 1 ? 1 : y2;
}
/* clip features between two vertical or horizontal axis-parallel lines:
* | |
* ___|___ | /
* / | \____|____/
* | |
*
* k1 and k2 are the line coordinates
* axis: 0 for x, 1 for y
* minAll and maxAll: minimum and maximum coordinate value for all features
*/
function clip(features, scale, k1, k2, axis, minAll, maxAll, options) {
k1 /= scale;
k2 /= scale;
if (minAll >= k1 && maxAll < k2) return features; // trivial accept
else if (maxAll < k1 || minAll >= k2) return null; // trivial reject
const clipped = [];
for (const feature of features) {
const geometry = feature.geometry;
let type = feature.type;
const min = axis === 0 ? feature.minX : feature.minY;
const max = axis === 0 ? feature.maxX : feature.maxY;
if (min >= k1 && max < k2) { // trivial accept
clipped.push(feature);
continue;
} else if (max < k1 || min >= k2) { // trivial reject
continue;
}
let newGeometry = [];
if (type === 'Point' || type === 'MultiPoint') {
clipPoints(geometry, newGeometry, k1, k2, axis);
} else if (type === 'LineString') {
clipLine(geometry, newGeometry, k1, k2, axis, false, options.lineMetrics);
} else if (type === 'MultiLineString') {
clipLines(geometry, newGeometry, k1, k2, axis, false);
} else if (type === 'Polygon') {
clipLines(geometry, newGeometry, k1, k2, axis, true);
} else if (type === 'MultiPolygon') {
for (const polygon of geometry) {
const newPolygon = [];
clipLines(polygon, newPolygon, k1, k2, axis, true);
if (newPolygon.length) {
newGeometry.push(newPolygon);
}
}
}
if (newGeometry.length) {
if (options.lineMetrics && type === 'LineString') {
for (const line of newGeometry) {
clipped.push(createFeature(feature.id, type, line, feature.tags));
}
continue;
}
if (type === 'LineString' || type === 'MultiLineString') {
if (newGeometry.length === 1) {
type = 'LineString';
newGeometry = newGeometry[0];
} else {
type = 'MultiLineString';
}
}
if (type === 'Point' || type === 'MultiPoint') {
type = newGeometry.length === 3 ? 'Point' : 'MultiPoint';
}
clipped.push(createFeature(feature.id, type, newGeometry, feature.tags));
}
}
return clipped.length ? clipped : null;
}
function clipPoints(geom, newGeom, k1, k2, axis) {
for (let i = 0; i < geom.length; i += 3) {
const a = geom[i + axis];
if (a >= k1 && a <= k2) {
addPoint(newGeom, geom[i], geom[i + 1], geom[i + 2]);
}
}
}
function clipLine(geom, newGeom, k1, k2, axis, isPolygon, trackMetrics) {
let slice = newSlice(geom);
const intersect = axis === 0 ? intersectX : intersectY;
let len = geom.start;
let segLen, t;
for (let i = 0; i < geom.length - 3; i += 3) {
const ax = geom[i];
const ay = geom[i + 1];
const az = geom[i + 2];
const bx = geom[i + 3];
const by = geom[i + 4];
const a = axis === 0 ? ax : ay;
const b = axis === 0 ? bx : by;
let exited = false;
if (trackMetrics) segLen = Math.sqrt(Math.pow(ax - bx, 2) + Math.pow(ay - by, 2));
if (a < k1) {
// ---|--> | (line enters the clip region from the left)
if (b > k1) {
t = intersect(slice, ax, ay, bx, by, k1);
if (trackMetrics) slice.start = len + segLen * t;
}
} else if (a > k2) {
// | <--|--- (line enters the clip region from the right)
if (b < k2) {
t = intersect(slice, ax, ay, bx, by, k2);
if (trackMetrics) slice.start = len + segLen * t;
}
} else {
addPoint(slice, ax, ay, az);
}
if (b < k1 && a >= k1) {
// <--|--- | or <--|-----|--- (line exits the clip region on the left)
t = intersect(slice, ax, ay, bx, by, k1);
exited = true;
}
if (b > k2 && a <= k2) {
// | ---|--> or ---|-----|--> (line exits the clip region on the right)
t = intersect(slice, ax, ay, bx, by, k2);
exited = true;
}
if (!isPolygon && exited) {
if (trackMetrics) slice.end = len + segLen * t;
newGeom.push(slice);
slice = newSlice(geom);
}
if (trackMetrics) len += segLen;
}
// add the last point
let last = geom.length - 3;
const ax = geom[last];
const ay = geom[last + 1];
const az = geom[last + 2];
const a = axis === 0 ? ax : ay;
if (a >= k1 && a <= k2) addPoint(slice, ax, ay, az);
// close the polygon if its endpoints are not the same after clipping
last = slice.length - 3;
if (isPolygon && last >= 3 && (slice[last] !== slice[0] || slice[last + 1] !== slice[1])) {
addPoint(slice, slice[0], slice[1], slice[2]);
}
// add the final slice
if (slice.length) {
newGeom.push(slice);
}
}
function newSlice(line) {
const slice = [];
slice.size = line.size;
slice.start = line.start;
slice.end = line.end;
return slice;
}
function clipLines(geom, newGeom, k1, k2, axis, isPolygon) {
for (const line of geom) {
clipLine(line, newGeom, k1, k2, axis, isPolygon, false);
}
}
function addPoint(out, x, y, z) {
out.push(x, y, z);
}
function intersectX(out, ax, ay, bx, by, x) {
const t = (x - ax) / (bx - ax);
addPoint(out, x, ay + (by - ay) * t, 1);
return t;
}
function intersectY(out, ax, ay, bx, by, y) {
const t = (y - ay) / (by - ay);
addPoint(out, ax + (bx - ax) * t, y, 1);
return t;
}
function wrap(features, options) {
const buffer = options.buffer / options.extent;
let merged = features;
const left = clip(features, 1, -1 - buffer, buffer, 0, -1, 2, options); // left world copy
const right = clip(features, 1, 1 - buffer, 2 + buffer, 0, -1, 2, options); // right world copy
if (left || right) {
merged = clip(features, 1, -buffer, 1 + buffer, 0, -1, 2, options) || []; // center world copy
if (left) merged = shiftFeatureCoords(left, 1).concat(merged); // merge left into center
if (right) merged = merged.concat(shiftFeatureCoords(right, -1)); // merge right into center
}
return merged;
}
function shiftFeatureCoords(features, offset) {
const newFeatures = [];
for (let i = 0; i < features.length; i++) {
const feature = features[i];
const type = feature.type;
let newGeometry;
if (type === 'Point' || type === 'MultiPoint' || type === 'LineString') {
newGeometry = shiftCoords(feature.geometry, offset);
} else if (type === 'MultiLineString' || type === 'Polygon') {
newGeometry = [];
for (const line of feature.geometry) {
newGeometry.push(shiftCoords(line, offset));
}
} else if (type === 'MultiPolygon') {
newGeometry = [];
for (const polygon of feature.geometry) {
const newPolygon = [];
for (const line of polygon) {
newPolygon.push(shiftCoords(line, offset));
}
newGeometry.push(newPolygon);
}
}
newFeatures.push(createFeature(feature.id, type, newGeometry, feature.tags));
}
return newFeatures;
}
function shiftCoords(points, offset) {
const newPoints = [];
newPoints.size = points.size;
if (points.start !== undefined) {
newPoints.start = points.start;
newPoints.end = points.end;
}
for (let i = 0; i < points.length; i += 3) {
newPoints.push(points[i] + offset, points[i + 1], points[i + 2]);
}
return newPoints;
}
// Transforms the coordinates of each feature in the given tile from
// mercator-projected space into (extent x extent) tile space.
function transformTile(tile, extent) {
if (tile.transformed) return tile;
const z2 = 1 << tile.z;
const tx = tile.x;
const ty = tile.y;
for (const feature of tile.features) {
const geom = feature.geometry;
const type = feature.type;
feature.geometry = [];
if (type === 1) {
for (let j = 0; j < geom.length; j += 2) {
feature.geometry.push(transformPoint(geom[j], geom[j + 1], extent, z2, tx, ty));
}
} else {
for (let j = 0; j < geom.length; j++) {
const ring = [];
for (let k = 0; k < geom[j].length; k += 2) {
ring.push(transformPoint(geom[j][k], geom[j][k + 1], extent, z2, tx, ty));
}
feature.geometry.push(ring);
}
}
}
tile.transformed = true;
return tile;
}
function transformPoint(x, y, extent, z2, tx, ty) {
return [
Math.round(extent * (x * z2 - tx)),
Math.round(extent * (y * z2 - ty))];
}
function createTile(features, z, tx, ty, options) {
const tolerance = z === options.maxZoom ? 0 : options.tolerance / ((1 << z) * options.extent);
const tile = {
features: [],
numPoints: 0,
numSimplified: 0,
numFeatures: features.length,
source: null,
x: tx,
y: ty,
z,
transformed: false,
minX: 2,
minY: 1,
maxX: -1,
maxY: 0
};
for (const feature of features) {
addFeature(tile, feature, tolerance, options);
}
return tile;
}
function addFeature(tile, feature, tolerance, options) {
const geom = feature.geometry;
const type = feature.type;
const simplified = [];
tile.minX = Math.min(tile.minX, feature.minX);
tile.minY = Math.min(tile.minY, feature.minY);
tile.maxX = Math.max(tile.maxX, feature.maxX);
tile.maxY = Math.max(tile.maxY, feature.maxY);
if (type === 'Point' || type === 'MultiPoint') {
for (let i = 0; i < geom.length; i += 3) {
simplified.push(geom[i], geom[i + 1]);
tile.numPoints++;
tile.numSimplified++;
}
} else if (type === 'LineString') {
addLine(simplified, geom, tile, tolerance, false, false);
} else if (type === 'MultiLineString' || type === 'Polygon') {
for (let i = 0; i < geom.length; i++) {
addLine(simplified, geom[i], tile, tolerance, type === 'Polygon', i === 0);
}
} else if (type === 'MultiPolygon') {
for (let k = 0; k < geom.length; k++) {
const polygon = geom[k];
for (let i = 0; i < polygon.length; i++) {
addLine(simplified, polygon[i], tile, tolerance, true, i === 0);
}
}
}
if (simplified.length) {
let tags = feature.tags || null;
if (type === 'LineString' && options.lineMetrics) {
tags = {};
for (const key in feature.tags) tags[key] = feature.tags[key];
tags['mapbox_clip_start'] = geom.start / geom.size;
tags['mapbox_clip_end'] = geom.end / geom.size;
}
const tileFeature = {
geometry: simplified,
type: type === 'Polygon' || type === 'MultiPolygon' ? 3 :
(type === 'LineString' || type === 'MultiLineString' ? 2 : 1),
tags
};
if (feature.id !== null) {
tileFeature.id = feature.id;
}
tile.features.push(tileFeature);
}
}
function addLine(result, geom, tile, tolerance, isPolygon, isOuter) {
const sqTolerance = tolerance * tolerance;
if (tolerance > 0 && (geom.size < (isPolygon ? sqTolerance : tolerance))) {
tile.numPoints += geom.length / 3;
return;
}
const ring = [];
for (let i = 0; i < geom.length; i += 3) {
if (tolerance === 0 || geom[i + 2] > sqTolerance) {
tile.numSimplified++;
ring.push(geom[i], geom[i + 1]);
}
tile.numPoints++;
}
if (isPolygon) rewind(ring, isOuter);
result.push(ring);
}
function rewind(ring, clockwise) {
let area = 0;
for (let i = 0, len = ring.length, j = len - 2; i < len; j = i, i += 2) {
area += (ring[i] - ring[j]) * (ring[i + 1] + ring[j + 1]);
}
if (area > 0 === clockwise) {
for (let i = 0, len = ring.length; i < len / 2; i += 2) {
const x = ring[i];
const y = ring[i + 1];
ring[i] = ring[len - 2 - i];
ring[i + 1] = ring[len - 1 - i];
ring[len - 2 - i] = x;
ring[len - 1 - i] = y;
}
}
}
const defaultOptions = {
maxZoom: 14, // max zoom to preserve detail on
indexMaxZoom: 5, // max zoom in the tile index
indexMaxPoints: 100000, // max number of points per tile in the tile index
tolerance: 3, // simplification tolerance (higher means simpler)
extent: 4096, // tile extent
buffer: 64, // tile buffer on each side
lineMetrics: false, // whether to calculate line metrics
promoteId: null, // name of a feature property to be promoted to feature.id
generateId: false, // whether to generate feature ids. Cannot be used with promoteId
debug: 0 // logging level (0, 1 or 2)
};
class GeoJSONVT {
constructor(data, options) {
options = this.options = extend(Object.create(defaultOptions), options);
const debug = options.debug;
if (debug) console.time('preprocess data');
if (options.maxZoom < 0 || options.maxZoom > 24) throw new Error('maxZoom should be in the 0-24 range');
if (options.promoteId && options.generateId) throw new Error('promoteId and generateId cannot be used together.');
// projects and adds simplification info
let features = convert(data, options);
// tiles and tileCoords are part of the public API
this.tiles = {};
this.tileCoords = [];
if (debug) {
console.timeEnd('preprocess data');
console.log('index: maxZoom: %d, maxPoints: %d', options.indexMaxZoom, options.indexMaxPoints);
console.time('generate tiles');
this.stats = {};
this.total = 0;
}
// wraps features (ie extreme west and extreme east)
features = wrap(features, options);
// start slicing from the top tile down
if (features.length) this.splitTile(features, 0, 0, 0);
if (debug) {
if (features.length) console.log('features: %d, points: %d', this.tiles[0].numFeatures, this.tiles[0].numPoints);
console.timeEnd('generate tiles');
console.log('tiles generated:', this.total, JSON.stringify(this.stats));
}
}
// splits features from a parent tile to sub-tiles.
// z, x, and y are the coordinates of the parent tile
// cz, cx, and cy are the coordinates of the target tile
//
// If no target tile is specified, splitting stops when we reach the maximum
// zoom or the number of points is low as specified in the options.
splitTile(features, z, x, y, cz, cx, cy) {
const stack = [features, z, x, y];
const options = this.options;
const debug = options.debug;
// avoid recursion by using a processing queue
while (stack.length) {
y = stack.pop();
x = stack.pop();
z = stack.pop();
features = stack.pop();
const z2 = 1 << z;
const id = toID(z, x, y);
let tile = this.tiles[id];
if (!tile) {
if (debug > 1) console.time('creation');
tile = this.tiles[id] = createTile(features, z, x, y, options);
this.tileCoords.push({z, x, y});
if (debug) {
if (debug > 1) {
console.log('tile z%d-%d-%d (features: %d, points: %d, simplified: %d)',
z, x, y, tile.numFeatures, tile.numPoints, tile.numSimplified);
console.timeEnd('creation');
}
const key = `z${ z}`;
this.stats[key] = (this.stats[key] || 0) + 1;
this.total++;
}
}
// save reference to original geometry in tile so that we can drill down later if we stop now
tile.source = features;
// if it's the first-pass tiling
if (cz == null) {
// stop tiling if we reached max zoom, or if the tile is too simple
if (z === options.indexMaxZoom || tile.numPoints <= options.indexMaxPoints) continue;
// if a drilldown to a specific tile
} else if (z === options.maxZoom || z === cz) {
// stop tiling if we reached base zoom or our target tile zoom
continue;
} else if (cz != null) {
// stop tiling if it's not an ancestor of the target tile
const zoomSteps = cz - z;
if (x !== cx >> zoomSteps || y !== cy >> zoomSteps) continue;
}
// if we slice further down, no need to keep source geometry
tile.source = null;
if (features.length === 0) continue;
if (debug > 1) console.time('clipping');
// values we'll use for clipping
const k1 = 0.5 * options.buffer / options.extent;
const k2 = 0.5 - k1;
const k3 = 0.5 + k1;
const k4 = 1 + k1;
let tl = null;
let bl = null;
let tr = null;
let br = null;
let left = clip(features, z2, x - k1, x + k3, 0, tile.minX, tile.maxX, options);
let right = clip(features, z2, x + k2, x + k4, 0, tile.minX, tile.maxX, options);
features = null;
if (left) {
tl = clip(left, z2, y - k1, y + k3, 1, tile.minY, tile.maxY, options);
bl = clip(left, z2, y + k2, y + k4, 1, tile.minY, tile.maxY, options);
left = null;
}
if (right) {
tr = clip(right, z2, y - k1, y + k3, 1, tile.minY, tile.maxY, options);
br = clip(right, z2, y + k2, y + k4, 1, tile.minY, tile.maxY, options);
right = null;
}
if (debug > 1) console.timeEnd('clipping');
stack.push(tl || [], z + 1, x * 2, y * 2);
stack.push(bl || [], z + 1, x * 2, y * 2 + 1);
stack.push(tr || [], z + 1, x * 2 + 1, y * 2);
stack.push(br || [], z + 1, x * 2 + 1, y * 2 + 1);
}
}
getTile(z, x, y) {
z = +z;
x = +x;
y = +y;
const options = this.options;
const {extent, debug} = options;
if (z < 0 || z > 24) return null;
const z2 = 1 << z;
x = (x + z2) & (z2 - 1); // wrap tile x coordinate
const id = toID(z, x, y);
if (this.tiles[id]) return transformTile(this.tiles[id], extent);
if (debug > 1) console.log('drilling down to z%d-%d-%d', z, x, y);
let z0 = z;
let x0 = x;
let y0 = y;
let parent;
while (!parent && z0 > 0) {
z0--;
x0 = x0 >> 1;
y0 = y0 >> 1;
parent = this.tiles[toID(z0, x0, y0)];
}
if (!parent || !parent.source) return null;
// if we found a parent tile containing the original geometry, we can drill down from it
if (debug > 1) {
console.log('found parent tile z%d-%d-%d', z0, x0, y0);
console.time('drilling down');
}
this.splitTile(parent.source, z0, x0, y0, z, x, y);
if (debug > 1) console.timeEnd('drilling down');
return this.tiles[id] ? transformTile(this.tiles[id], extent) : null;
}
}
function toID(z, x, y) {
return (((1 << z) * y + x) * 32) + z;
}
function extend(dest, src) {
for (const i in src) dest[i] = src[i];
return dest;
}
function geojsonvt(data, options) {
return new GeoJSONVT(data, options);
}
return geojsonvt;
}));