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mhammercmhammerc
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feat: implement pointToLineDistance (#189)
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‎Progress.md‎

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@@ -20,7 +20,7 @@ Dart. This is an on going project and functions are being added once needed. If
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- [x] [midpoint](https://github.com/dartclub/turf_dart/blob/main/lib/src/midpoint.dart)
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- [ ] pointOnFeature
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- [ ] polygonTangents
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- [ ] pointToLineDistance
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- [x] [pointToLineDistance](https://github.com/dartclub/turf_dart/blob/main/lib/src/point_to_line_distance.dart)
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- [x] [rhumbBearing](https://github.com/dartclub/turf_dart/blob/main/lib/src/rhumb_bearing.dart)
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- [x] [rhumbDestination](https://github.com/dartclub/turf_dart/blob/main/lib/src/rhumb_destination.dart)
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- [x] [rhumbDistance](https://github.com/dartclub/turf_dart/blob/main/lib/src/rhumb_distance.dart)

‎lib/point_to_line_distance.dart‎

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library turf_point_to_line_distance;
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export 'package:geotypes/geotypes.dart';
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export 'src/point_to_line_distance.dart';

‎lib/src/helpers.dart‎

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@@ -31,6 +31,18 @@ enum Corner {
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centroid,
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}
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/// Whether to calculate the distance based on geodesic (spheroid) or
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/// planar (flat) method.
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enum DistanceGeometry {
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/// Calculations will be made on a 2D plane, NOT taking into account the
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/// earth curvature.
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planar,
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/// Calculate the distance with geodesic (spheroid) equations. It will take
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/// into account the earth as a sphere.
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geodesic,
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}
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/// Earth Radius used with the Harvesine formula and approximates using a spherical (non-ellipsoid) Earth.
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const earthRadius = 6371008.8;
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‎lib/src/point_to_line_distance.dart‎

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import 'package:turf/distance.dart';
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import 'package:turf/line_segment.dart';
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import 'helpers.dart';
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// Sourced from https://turfjs.org (MIT license) and from
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// http://geomalgorithms.com/a02-_lines.html
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/// Returns the minimum distance between a [point] and a [line], being the
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/// distance from a line the minimum distance between the point and any
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/// segment of the [LineString].
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///
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/// Example:
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/// ```dart
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/// final point = Point(coordinates: Position(0, 0));
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/// final line = LineString(coordinates: [Position(1, 1), Position(-1, 1)]);
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///
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/// final distance = pointToLineDistance(point, line, unit: Unit.miles);
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/// // distance == 69.11854715938406
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/// ```
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num pointToLineDistance(
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Point point,
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LineString line, {
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Unit unit = Unit.kilometers,
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DistanceGeometry method = DistanceGeometry.geodesic,
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}) {
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var distance = double.infinity;
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final position = point.coordinates;
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segmentEach(line, (segment, _, __, ___, ____) {
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final a = segment.geometry!.coordinates[0];
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final b = segment.geometry!.coordinates[1];
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final d = _distanceToSegment(position, a, b, method: method);
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if (d < distance) {
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distance = d.toDouble();
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}
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});
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return convertLength(distance, Unit.degrees, unit);
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}
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/// Returns the distance between a point P on a segment AB.
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num _distanceToSegment(
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Position p,
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Position a,
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Position b, {
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required DistanceGeometry method,
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}) {
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final v = b - a;
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final w = p - a;
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final c1 = w.dotProduct(v);
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if (c1 <= 0) {
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return _calcDistance(p, a, method: method, unit: Unit.degrees);
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}
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final c2 = v.dotProduct(v);
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if (c2 <= c1) {
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return _calcDistance(p, b, method: method, unit: Unit.degrees);
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}
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final b2 = c1 / c2;
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final pb = a + Position(v[0]! * b2, v[1]! * b2);
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return _calcDistance(p, pb, method: method, unit: Unit.degrees);
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}
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num _calcDistance(
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Position a,
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Position b, {
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required Unit unit,
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required DistanceGeometry method,
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}) {
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if (method == DistanceGeometry.planar) {
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return rhumbDistance(Point(coordinates: a), Point(coordinates: b), unit);
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}
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// Otherwise DistanceGeometry.geodesic
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return distanceRaw(a, b, unit);
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}

‎lib/turf.dart‎

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@@ -27,6 +27,7 @@ export 'meta.dart';
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export 'midpoint.dart';
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export 'nearest_point_on_line.dart';
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export 'nearest_point.dart';
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export 'point_to_line_distance.dart';
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export 'polygon_smooth.dart';
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export 'polygon_to_line.dart';
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export 'polyline.dart';

‎test/components/point_to_line_distance_test.dart‎

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import 'dart:convert';
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import 'dart:io';
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import 'package:test/test.dart';
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import 'package:turf/helpers.dart';
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import 'package:turf/src/point_to_line_distance.dart';
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final distances = {
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"city-line1.geojson": 1.0299686758,
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"city-line2.geojson": 3.6186172981,
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"city-segment-inside1.geojson": 1.1489389115,
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"city-segment-inside2.geojson": 1.0280898152,
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"city-segment-inside3.geojson": 3.5335695907,
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"city-segment-obtuse1.geojson": 2.8573246363,
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"city-segment-obtuse2.geojson": 3.3538913334,
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"city-segment-projected1.geojson": 3.5886611693,
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"city-segment-projected2.geojson": 4.163469898,
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"issue-1156.geojson": 189.6618028794,
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"line-fiji.geojson": 27.1266612008,
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"line-resolute-bay.geojson": 425.0745081528,
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"line1.geojson": 23.4224834672,
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"line2.geojson": 188.015686924,
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"segment-fiji.geojson": 27.6668301762,
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"segment1.geojson": 69.0934195756,
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"segment1a.geojson": 69.0934195756,
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"segment2.geojson": 69.0934195756,
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"segment3.geojson": 69.0828960461,
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"segment4.geojson": 332.8803863574
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};
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void main() {
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group('pointToLineDistance', () {
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group('in == out', () {
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final inDir = Directory('./test/examples/point_to_line_distance/in');
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for (final file in inDir.listSync(recursive: true)) {
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if (file is File && file.path.endsWith('.geojson')) {
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testFile(file);
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}
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}
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});
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group('unit tests', () {
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testPlanarGeodesic();
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});
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});
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}
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void testFile(File file) {
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test(file.path, () {
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final inSource = file.readAsStringSync();
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final collection = FeatureCollection.fromJson(jsonDecode(inSource));
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final rawPoint = collection.features[0];
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final rawLine = collection.features[1];
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final point = Feature<Point>.fromJson(rawPoint.toJson());
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final line = Feature<LineString>.fromJson(rawLine.toJson());
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final properties = rawPoint.properties ?? {};
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final unitRaw = properties["units"] as String?;
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var unit = Unit.kilometers;
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if (unitRaw == 'meters') {
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unit = Unit.meters;
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} else if (unitRaw == 'miles') {
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unit = Unit.miles;
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} else {
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expect(unitRaw, null, reason: '"units" was given but not handled.');
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}
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final distance =
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pointToLineDistance(point.geometry!, line.geometry!, unit: unit);
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final name = file.path.substring(file.path.lastIndexOf('/') + 1);
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expect(distance, closeTo(distances[name]!, 0.01));
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});
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}
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void testPlanarGeodesic() {
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test('Check planar and geodesic results are different', () {
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final pt = Point(coordinates: Position(0, 0));
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final line = LineString(coordinates: [
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Position(10, 10),
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Position(-1, 1),
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]);
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final geoOut =
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pointToLineDistance(pt, line, method: DistanceGeometry.geodesic);
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final planarOut =
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pointToLineDistance(pt, line, method: DistanceGeometry.planar);
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expect(geoOut, isNot(equals(planarOut)));
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});
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}

‎test/examples/point_to_line_distance/in/city-line1.geojson‎

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{
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"type": "FeatureCollection",
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"features": [
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{
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"type": "Feature",
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"properties": {},
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"geometry": {
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"type": "Point",
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"coordinates": [-0.3767967224121093, 39.4689324766527]
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}
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},
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{
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"type": "Feature",
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"properties": {},
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"geometry": {
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"type": "LineString",
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"coordinates": [
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[-0.40567874908447266, 39.47386857192064],
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[-0.3963661193847656, 39.47578991028725],
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[-0.38035869598388666, 39.482216070269594],
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[-0.3776121139526367, 39.48195108571802],
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[-0.3689002990722656, 39.47641930269614],
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[-0.35945892333984375, 39.46349905420083],
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[-0.35782814025878906, 39.45982131412374],
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[-0.3458118438720703, 39.453890134716616]
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]
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}
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}
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]
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}

‎test/examples/point_to_line_distance/in/city-line2.geojson‎

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{
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"type": "FeatureCollection",
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"features": [
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{
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"type": "Feature",
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"properties": {},
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"geometry": {
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"type": "Point",
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"coordinates": [-3.592529296875, 40.573804799488194]
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}
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},
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{
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"type": "Feature",
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"properties": {},
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"geometry": {
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"type": "LineString",
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"coordinates": [
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[-3.8884735107421875, 40.420292132688964],
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[-3.736724853515625, 40.276906410822825],
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[-3.5025787353515625, 40.422383097039905],
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[-3.5018920898437496, 40.516409213865586],
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[-3.668060302734375, 40.559199680578075]
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]
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}
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}
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]
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}

‎test/examples/point_to_line_distance/in/city-segment-inside1.geojson‎

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{
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"type": "FeatureCollection",
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"features": [
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{
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"type": "Feature",
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"properties": {
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"units": "miles"
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},
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"geometry": {
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"type": "Point",
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"coordinates": [-6.0047149658203125, 37.365109304227246]
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}
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},
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{
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"type": "Feature",
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"properties": {},
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"geometry": {
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"type": "LineString",
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"coordinates": [
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[-6.0150146484375, 37.38011551844836],
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[-5.931415557861328, 37.39702801486944]
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]
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}
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}
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]
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}

‎test/examples/point_to_line_distance/in/city-segment-inside2.geojson‎

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{
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"type": "FeatureCollection",
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"features": [
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{
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"type": "Feature",
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"properties": {},
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"geometry": {
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"type": "Point",
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"coordinates": [-0.3767967224121093, 39.4689324766527]
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}
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},
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{
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"type": "Feature",
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"properties": {},
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"geometry": {
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"type": "LineString",
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"coordinates": [
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[-0.3689861297607422, 39.47648555419739],
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[-0.3595447540283203, 39.46363158174706]
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]
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}
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}
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]
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}

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