turftracker/frontend/node_modules/@turf/polygon-tangents/dist/es/index.js

import { getCoords, getType } from '@turf/invariant';
import { featureCollection, point } from '@turf/helpers';
import calcBbox from '@turf/bbox';
import explode from '@turf/explode';
import nearestPoint from '@turf/nearest-point';

/**
 * Finds the tangents of a {@link Polygon|(Multi)Polygon} from a {@link Point}.
 *
 * @name polygonTangents
 * @param {Coord} pt to calculate the tangent points from
 * @param {Feature<Polygon|MultiPolygon>} polygon to get tangents from
 * @returns {FeatureCollection<Point>} Feature Collection containing the two tangent points
 * @example
 * var polygon = turf.polygon([[[11, 0], [22, 4], [31, 0], [31, 11], [21, 15], [11, 11], [11, 0]]]);
 * var point = turf.point([61, 5]);
 *
 * var tangents = turf.polygonTangents(point, polygon)
 *
 * //addToMap
 * var addToMap = [tangents, point, polygon];
 */
function polygonTangents(pt, polygon) {
  var pointCoords = getCoords(pt);
  var polyCoords = getCoords(polygon);

  var rtan;
  var ltan;
  var enext;
  var eprev;
  var bbox = calcBbox(polygon);
  var nearestPtIndex = 0;
  var nearest = null;

  // If the point lies inside the polygon bbox then we need to be a bit trickier
  // otherwise points lying inside reflex angles on concave polys can have issues
  if (
    pointCoords[0] > bbox[0] &&
    pointCoords[0] < bbox[2] &&
    pointCoords[1] > bbox[1] &&
    pointCoords[1] < bbox[3]
  ) {
    nearest = nearestPoint(pt, explode(polygon));
    nearestPtIndex = nearest.properties.featureIndex;
  }
  var type = getType(polygon);
  switch (type) {
    case "Polygon":
      rtan = polyCoords[0][nearestPtIndex];
      ltan = polyCoords[0][0];
      if (nearest !== null) {
        if (nearest.geometry.coordinates[1] < pointCoords[1])
          ltan = polyCoords[0][nearestPtIndex];
      }
      eprev = isLeft(
        polyCoords[0][0],
        polyCoords[0][polyCoords[0].length - 1],
        pointCoords
      );
      var out = processPolygon(
        polyCoords[0],
        pointCoords,
        eprev,
        enext,
        rtan,
        ltan);
      rtan = out[0];
      ltan = out[1];
      break;
    case "MultiPolygon":
      var closestFeature = 0;
      var closestVertex = 0;
      var verticesCounted = 0;
      for (var i = 0; i < polyCoords[0].length; i++) {
        closestFeature = i;
        var verticeFound = false;
        for (var i2 = 0; i2 < polyCoords[0][i].length; i2++) {
          closestVertex = i2;
          if (verticesCounted === nearestPtIndex) {
            verticeFound = true;
            break;
          }
          verticesCounted++;
        }
        if (verticeFound) break;
      }
      rtan = polyCoords[0][closestFeature][closestVertex];
      ltan = polyCoords[0][closestFeature][closestVertex];
      eprev = isLeft(
        polyCoords[0][0][0],
        polyCoords[0][0][polyCoords[0][0].length - 1],
        pointCoords
      );
      polyCoords.forEach(function (ring) {
        var out = processPolygon(
          ring[0],
          pointCoords,
          eprev,
          enext,
          rtan,
          ltan);
        rtan = out[0];
        ltan = out[1];
      });
      break;
  }
  return featureCollection([point(rtan), point(ltan)]);
}

function processPolygon(polygonCoords, ptCoords, eprev, enext, rtan, ltan) {
  for (var i = 0; i < polygonCoords.length; i++) {
    var currentCoords = polygonCoords[i];
    var nextCoordPair = polygonCoords[i + 1];
    if (i === polygonCoords.length - 1) {
      nextCoordPair = polygonCoords[0];
    }
    enext = isLeft(currentCoords, nextCoordPair, ptCoords);
    if (eprev <= 0 && enext > 0) {
      if (!isBelow(ptCoords, currentCoords, rtan)) {
        rtan = currentCoords;
      }
    } else if (eprev > 0 && enext <= 0) {
      if (!isAbove(ptCoords, currentCoords, ltan)) {
        ltan = currentCoords;
      }
    }
    eprev = enext;
  }
  return [rtan, ltan];
}

function isAbove(point1, point2, point3) {
  return isLeft(point1, point2, point3) > 0;
}

function isBelow(point1, point2, point3) {
  return isLeft(point1, point2, point3) < 0;
}

function isLeft(point1, point2, point3) {
  return (
    (point2[0] - point1[0]) * (point3[1] - point1[1]) -
    (point3[0] - point1[0]) * (point2[1] - point1[1])
  );
}

export default polygonTangents;