vega-geo/src/GeoJSON.js

Geographic data transforms for Vega dataflows.

import {Feature, FeatureCollection, MultiPoint} from './constants.js';
import {Transform} from 'vega-dataflow';
import {accessorFields, identity, inherits} from 'vega-util';

/**
 * Consolidate an array of [longitude, latitude] points or GeoJSON features
 * into a combined GeoJSON object. This transform is particularly useful for
 * combining geo data for a Projection's fit argument. The resulting GeoJSON
 * data is available as this transform's value. Input pulses are unchanged.
 * @constructor
 * @param {object} params - The parameters for this operator.
 * @param {Array<function(object): *>} [params.fields] - A two-element array
 *   of field accessors for the longitude and latitude values.
 * @param {function(object): *} params.geojson - A field accessor for
 *   retrieving GeoJSON feature data.
 */
export default function GeoJSON(params) {
  Transform.call(this, null, params);
}

GeoJSON.Definition = {
  'type': 'GeoJSON',
  'metadata': {},
  'params': [
    { 'name': 'fields', 'type': 'field', 'array': true, 'length': 2 },
    { 'name': 'geojson', 'type': 'field' }
  ]
};

inherits(GeoJSON, Transform, {
  transform(_, pulse) {
    var features = this._features,
        points = this._points,
        fields = _.fields,
        lon = fields && fields[0],
        lat = fields && fields[1],
        geojson = _.geojson || (!fields && identity),
        flag = pulse.ADD,
        mod;

    mod = _.modified()
      || pulse.changed(pulse.REM)
      || pulse.modified(accessorFields(geojson))
      || (lon && (pulse.modified(accessorFields(lon))))
      || (lat && (pulse.modified(accessorFields(lat))));

    if (!this.value || mod) {
      flag = pulse.SOURCE;
      this._features = (features = []);
      this._points = (points = []);
    }

    if (geojson) {
      pulse.visit(flag, t => features.push(geojson(t)));
    }

    if (lon && lat) {
      pulse.visit(flag, t => {
        var x = lon(t),
            y = lat(t);
        if (x != null && y != null && (x = +x) === x && (y = +y) === y) {
          points.push([x, y]);
        }
      });
      features = features.concat({
        type: Feature,
        geometry: {
          type: MultiPoint,
          coordinates: points
        }
      });
    }

    this.value = {
      type: FeatureCollection,
      features: features
    };
  }
});