@loaders.gl/mvt
Version:
Loader for Mapbox Vector Tiles
139 lines • 4.88 kB
JavaScript
// loaders.gl
// SPDX-License-Identifier: MIT
// Copyright (c) vis.gl contributors
// Forked from https://github.com/mapbox/geojson-vt under compatible ISC license
/**
* Create a tile from features and tile index
*/
export function createProtoTile(features, z, tx, ty, options) {
const tolerance = z === options.maxZoom ? 0 : options.tolerance / ((1 << z) * options.extent);
const tile = {
protoFeatures: [],
sourceFeatures: null,
numPoints: 0,
numSimplified: 0,
numFeatures: features.length,
x: tx,
y: ty,
z,
transformed: false,
minX: 2,
minY: 1,
maxX: -1,
maxY: 0
};
for (const feature of features) {
addProtoFeature(tile, feature, tolerance, options);
}
return tile;
}
// eslint-disable-next-line complexity, max-statements
function addProtoFeature(tile, feature, tolerance, options) {
const geometry = feature.geometry;
const type = feature.type;
const simplifiedGeometry = [];
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);
let simplifiedType;
switch (type) {
case 'Point':
case 'MultiPoint':
simplifiedType = 1;
for (let i = 0; i < geometry.length; i += 3) {
simplifiedGeometry.push(geometry[i], geometry[i + 1]);
tile.numPoints++;
tile.numSimplified++;
}
break;
case 'LineString':
simplifiedType = 2;
addProtoLine(simplifiedGeometry, geometry, tile, tolerance, false, false);
break;
case 'MultiLineString':
simplifiedType = 2;
for (let i = 0; i < geometry.length; i++) {
addProtoLine(simplifiedGeometry, geometry[i], tile, tolerance, false, i === 0);
}
break;
case 'Polygon':
simplifiedType = 3;
for (let i = 0; i < geometry.length; i++) {
addProtoLine(simplifiedGeometry, geometry[i], tile, tolerance, true, i === 0);
}
break;
case 'MultiPolygon':
simplifiedType = 3;
for (let k = 0; k < geometry.length; k++) {
const polygon = geometry[k];
for (let i = 0; i < polygon.length; i++) {
addProtoLine(simplifiedGeometry, polygon[i], tile, tolerance, true, i === 0);
}
}
break;
default:
throw new Error(`Unknown geometry type: ${type}`);
}
if (simplifiedGeometry.length) {
let tags = feature.tags || null;
if (type === 'LineString' && options.lineMetrics) {
tags = {};
for (const key in feature.tags) {
tags[key] = feature.tags[key];
}
// @ts-expect-error adding fields to arrays
// eslint-disable-next-line camelcase
tags.mapbox_clip_start = geometry.start / geometry.size;
// @ts-expect-error adding fields to arrays
// eslint-disable-next-line camelcase
tags.mapbox_clip_end = geometry.end / geometry.size;
}
const tileFeature = {
geometry: simplifiedGeometry,
simplifiedType,
// @ts-expect-error
tags
};
if (feature.id !== null) {
tileFeature.id = feature.id;
}
tile.protoFeatures.push(tileFeature);
}
}
// eslint-disable-next-line max-params, max-statements
function addProtoLine(result, geometry, tile, tolerance, isPolygon, isOuter) {
const sqTolerance = tolerance * tolerance;
if (tolerance > 0 && geometry.size < (isPolygon ? sqTolerance : tolerance)) {
tile.numPoints += geometry.length / 3;
return;
}
const ring = [];
for (let i = 0; i < geometry.length; i += 3) {
if (tolerance === 0 || geometry[i + 2] > sqTolerance) {
tile.numSimplified++;
ring.push(geometry[i], geometry[i + 1]);
}
tile.numPoints++;
}
if (isPolygon)
rewind(ring, isOuter);
result.push(ring);
}
function rewind(ring, clockwise) {
let area = 0;
for (let i = 0, j = ring.length - 2; i < ring.length; 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;
}
}
}
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