@loaders.gl/3d-tiles
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3D Tiles, an open standard for streaming massive heterogeneous 3D geospatial datasets.
61 lines • 2.47 kB
JavaScript
// loaders.gl
// SPDX-License-Identifier: MIT
// Copyright vis.gl contributors
import { IJToST, STToUV, FaceUVToXYZ, XYZToLngLat } from "../s2geometry/s2-geometry.js";
const MAX_RESOLUTION = 100;
/**
* Get a polygon with corner coordinates for an S2 cell
* @param s2cell {S2Cell} S2 cell
* @return {Float64Array} - a simple polygon in flat array format: [lng0, lat0, lng1, lat1, ...]
* - the polygon is closed, i.e. last coordinate is a copy of the first coordinate
*/
// eslint-disable-next-line max-statements
export function getS2BoundaryFlatFromS2Cell(s2cell) {
const { face, ij, level } = s2cell;
const offsets = [
[0, 0],
[0, 1],
[1, 1],
[1, 0],
[0, 0]
];
// The S2 cell edge is curved: http://s2geometry.io/
// This is more prominent at lower levels
// resolution is the number of segments to generate per edge.
// We exponentially reduce resolution as level increases so it doesn't affect perf
// when there are a large number of cells
const resolution = Math.max(1, Math.ceil(MAX_RESOLUTION * Math.pow(2, -level)));
const result = new Float64Array(4 * resolution * 2 + 2);
let ptIndex = 0;
let prevLng = 0;
for (let i = 0; i < 4; i++) {
const offset = offsets[i].slice(0);
const nextOffset = offsets[i + 1];
const stepI = (nextOffset[0] - offset[0]) / resolution;
const stepJ = (nextOffset[1] - offset[1]) / resolution;
for (let j = 0; j < resolution; j++) {
offset[0] += stepI;
offset[1] += stepJ;
// Cell can be represented by coordinates IJ, ST, UV, XYZ
// http://s2geometry.io/devguide/s2cell_hierarchy#coordinate-systems
const st = IJToST(ij, level, offset);
const uv = STToUV(st);
const xyz = FaceUVToXYZ(face, uv);
const lngLat = XYZToLngLat(xyz);
// Adjust longitude for Web Mercator projection
if (Math.abs(lngLat[1]) > 89.999) {
lngLat[0] = prevLng;
}
const deltaLng = lngLat[0] - prevLng;
lngLat[0] += deltaLng > 180 ? -360 : deltaLng < -180 ? 360 : 0;
result[ptIndex++] = lngLat[0];
result[ptIndex++] = lngLat[1];
prevLng = lngLat[0];
}
}
// close the loop
result[ptIndex++] = result[0];
result[ptIndex++] = result[1];
return result;
}
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