turf-line-dissolve.js

"use strict";
Object.defineProperty(exports, "__esModule", { value: true });
var clone_1 = require("@turf/clone");
var helpers_1 = require("@turf/helpers");
var invariant_1 = require("@turf/invariant");
var meta_1 = require("@turf/meta");
/**
 * Merges all connected (non-forking, non-junctioning) line strings into single lineStrings.
 * [LineString] -> LineString|MultiLineString
 *
 * @param {FeatureCollection<LineString|MultiLineString>} geojson Lines to dissolve
 * @param {Object} [options={}] Optional parameters
 * @param {boolean} [options.mutate=false] Prevent input mutation
 * @returns {Feature<LineString|MultiLineString>} Dissolved lines
 */
function lineDissolve(geojson, options) {
    if (options === void 0) { options = {}; }
    // Optional parameters
    options = options || {};
    if (!helpers_1.isObject(options)) {
        throw new Error("options is invalid");
    }
    var mutate = options.mutate;
    // Validation
    if (invariant_1.getType(geojson) !== "FeatureCollection") {
        throw new Error("geojson must be a FeatureCollection");
    }
    if (!geojson.features.length) {
        throw new Error("geojson is empty");
    }
    // Clone geojson to avoid side effects
    if (mutate === false || mutate === undefined) {
        geojson = clone_1.default(geojson);
    }
    var result = [];
    var lastLine = meta_1.lineReduce(geojson, function (previousLine, currentLine) {
        // Attempt to merge this LineString with the other LineStrings, updating
        // the reference as it is merged with others and grows.
        var merged = mergeLineStrings(previousLine, currentLine);
        // Accumulate the merged LineString
        if (merged) {
            return merged;
            // Put the unmerged LineString back into the list
        }
        else {
            result.push(previousLine);
            return currentLine;
        }
    });
    // Append the last line
    if (lastLine) {
        result.push(lastLine);
    }
    // Return null if no lines were dissolved
    if (!result.length) {
        return null;
        // Return LineString if only 1 line was dissolved
    }
    else if (result.length === 1) {
        return result[0];
        // Return MultiLineString if multiple lines were dissolved with gaps
    }
    else {
        return helpers_1.multiLineString(result.map(function (line) {
            return line.coordinates;
        }));
    }
}
// [Number, Number] -> String
function coordId(coord) {
    return coord[0].toString() + "," + coord[1].toString();
}
/**
 * LineString, LineString -> LineString
 *
 * @private
 * @param {Feature<LineString>} a line1
 * @param {Feature<LineString>} b line2
 * @returns {Feature<LineString>|null} Merged LineString
 */
function mergeLineStrings(a, b) {
    var coords1 = a.geometry.coordinates;
    var coords2 = b.geometry.coordinates;
    var s1 = coordId(coords1[0]);
    var e1 = coordId(coords1[coords1.length - 1]);
    var s2 = coordId(coords2[0]);
    var e2 = coordId(coords2[coords2.length - 1]);
    // TODO: handle case where more than one of these is true!
    var coords;
    if (s1 === e2) {
        coords = coords2.concat(coords1.slice(1));
    }
    else if (s2 === e1) {
        coords = coords1.concat(coords2.slice(1));
    }
    else if (s1 === s2) {
        coords = coords1.slice(1).reverse().concat(coords2);
    }
    else if (e1 === e2) {
        coords = coords1.concat(coords2.reverse().slice(1));
    }
    else {
        return null;
    }
    return helpers_1.lineString(coords);
}
exports.default = lineDissolve;