106 lines
3.4 KiB
JavaScript
Executable File
106 lines
3.4 KiB
JavaScript
Executable File
import clone from "@turf/clone";
|
|
import { isObject, lineString, multiLineString } from "@turf/helpers";
|
|
import { getType } from "@turf/invariant";
|
|
import { lineReduce } from "@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 (!isObject(options)) {
|
|
throw new Error("options is invalid");
|
|
}
|
|
var mutate = options.mutate;
|
|
// Validation
|
|
if (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(geojson);
|
|
}
|
|
var result = [];
|
|
var lastLine = 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 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 lineString(coords);
|
|
}
|
|
export default lineDissolve;
|