Source: simplify.js

  1. import { check } from "./helpers/check.js";
  2. import { topology } from "topojson-server";
  3. import { feature, quantize as quantiz } from "topojson-client";
  4. import { presimplify, quantile, simplify as simple } from "topojson-simplify";
  6. const topojson = Object.assign(
  7.   {},
  8.   { topology, presimplify, quantiz, quantile, simple, feature }
  9. );
  11. /**
  12.  * @function simplify
  13.  * @export
  14.  * @summary Simplify geometries. The `simplify()` function allows to simplify a geometry using <code>topojson-simplify</code> library. The parameter k difine the  The quantile of the simplification. By default, the generalization level is calculated automatically to ensure smooth map display.
  15.  * @description Based on `topojson.simplify`.
  16.  * @param {object|array} data - A GeoJSON FeatureCollection, an array of features, an array of geometries, a single feature or a single geometry.
  17.  * @param {object} options - Optional parameters
  18.  * @param {number} [options.k = undefined] - quantile of the simplification (from 0 to 1). If not defened, the generalization level is calculated automatically to ensure smooth map display.
  19.  * @param {number} [options.quantize = undefined] - A smaller quantizeAmount produces a smaller file. Typical values are between 1e4 and 1e6, although it depends on the resolution you want in the output file.
  20.  * @param {number} [options.arcs = 15000] - Instead of the k parameter, you can determine the level of generalization by targeting a specific number of arcs. The result will be an approximation.
  21.  * @returns {object|array} - A GeoJSON FeatureCollection, an array of features, an array of geometries, a single feature or a single geometry (it depends on what you've set as `data`).
  22.  * @example
  23.  * geotoolbox.simplify(*a geojson*, {k: 0.1})
  24.  */
  26. export function simplify(
  27.   data,
  28.   { k = undefined, quantize = undefined, arcs = 15000 } = {}
  29. ) {
  30.   const handle = check(data);
  31.   let x = handle.import(data);
  32.   let topo = topojson.topology({ foo: x });
  33.   let simpl = topojson.presimplify(topo);
  35.   if (k == undefined) {
  36.     k = arcs / simpl.arcs.flat().length;
  37.     k = k > 1 ? 1 : k;
  38.   }
  40.   simpl = topojson.simple(simpl, topojson.quantile(simpl, k));
  41.   if (quantize) {
  42.     simpl = topojson.quantiz(simpl, quantize);
  43.   }
  45.   x.features = topojson.feature(simpl, Object.keys(simpl.objects)[0]).features;
  46.   x.name = "simplify";
  47.   return handle.export(x);
  48. }