@kylebarron/snap-to-tin/lib/rtree.js

Snap vector features to the faces of a triangulated irregular network (TIN).

import Flatbush from "flatbush";
import { splitLine2d, triangleToBounds } from "./geom";
// Get triangles from terrain
export function constructRTree(indices, positions) {
    // Create list of objects for insertion into RTree
    const triangles = createTriangles(indices, positions);
    // initialize Flatbush for # of items
    // each triangle has 3 vertices of 3 coordinates each
    // 16 is default for nodeSize
    // store coordinates in flatbush internally as Float32Array
    const index = new Flatbush(triangles.length / 9, 16, Float32Array);
    // fill it with bounding boxes of triangles
    for (let i = 0; i < triangles.length / 9; i++) {
        const triangle = triangles.subarray(i * 9, (i + 1) * 9);
        const [minX, minY, maxX, maxY] = triangleToBounds(triangle);
        index.add(minX, minY, maxX, maxY);
    }
    // perform the indexing
    index.finish();
    return { index, triangles };
}
export function createTriangles(indices, positions) {
    const triangles = new Float32Array(indices.length * 3);
    for (let i = 0; i < indices.length; i += 3) {
        // The indices within `positions` of the three vertices of the triangle
        const aIndex = indices[i];
        const bIndex = indices[i + 1];
        const cIndex = indices[i + 2];
        // The three vertices of the triangle, where each vertex is an array of [x, y, z]
        const a = positions.subarray(aIndex * 3, (aIndex + 1) * 3);
        const b = positions.subarray(bIndex * 3, (bIndex + 1) * 3);
        const c = positions.subarray(cIndex * 3, (cIndex + 1) * 3);
        triangles.set(a, i * 3);
        triangles.set(b, (i + 1) * 3);
        triangles.set(c, (i + 2) * 3);
    }
    return triangles;
}
export function searchLineInIndex(line, index, maxPctArea = 0.01) {
    // Reduce total area searched in rtree to reduce false positives
    const indexArea = getIndexArea(index);
    const nSegments = getNumLineSegments(line, indexArea, maxPctArea);
    const lineSegments = splitLine2d(line, nSegments);
    const resultIndices = new Set();
    for (const lineSegment of lineSegments) {
        const [minX, minY] = lineSegment[0];
        const [maxX, maxY] = lineSegment[1];
        index
            .search(minX, minY, maxX, maxY)
            .forEach(item => resultIndices.add(item));
    }
    return Array.from(resultIndices);
}
export function getIndexArea(index) {
    let area;
    if (index.minX !== Infinity &&
        index.minY !== Infinity &&
        index.maxX !== -Infinity &&
        index.maxY !== -Infinity) {
        area = (index.maxX - index.minX) * (index.maxY - index.minY);
    }
    return area;
}
export function getNumLineSegments(line, indexArea, maxPctArea = 0.01) {
    if (!indexArea) {
        return 1;
    }
    const [minX, minY] = line[0];
    const [maxX, maxY] = line[1];
    const searchArea = (maxX - minX) * (maxY - minY);
    const pctSearch = searchArea / indexArea;
    return Math.max(1, Math.ceil(pctSearch / maxPctArea));
}