feat: implement pointToLineDistance (#189)

Progress.md

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

lib/point_to_line_distance.dart

@@ -0,0 +1,4 @@
+library turf_point_to_line_distance;
+
+export 'package:geotypes/geotypes.dart';
+export 'src/point_to_line_distance.dart';

lib/src/helpers.dart

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

lib/src/point_to_line_distance.dart

@@ -0,0 +1,79 @@
+import 'package:turf/distance.dart';
+import 'package:turf/line_segment.dart';
+import 'helpers.dart';
+
+// Sourced from https://turfjs.org (MIT license) and from
+// http://geomalgorithms.com/a02-_lines.html
+
+/// Returns the minimum distance between a [point] and a [line], being the
+/// distance from a line the minimum distance between the point and any
+/// segment of the [LineString].
+///
+/// Example:
+/// ```dart
+/// final point = Point(coordinates: Position(0, 0));
+/// final line = LineString(coordinates: [Position(1, 1), Position(-1, 1)]);
+///
+/// final distance = pointToLineDistance(point, line, unit: Unit.miles);
+/// // distance == 69.11854715938406
+/// ```
+num pointToLineDistance(
+  Point point,
+  LineString line, {
+  Unit unit = Unit.kilometers,
+  DistanceGeometry method = DistanceGeometry.geodesic,
+}) {
+  var distance = double.infinity;
+  final position = point.coordinates;
+
+  segmentEach(line, (segment, _, __, ___, ____) {
+    final a = segment.geometry!.coordinates[0];
+    final b = segment.geometry!.coordinates[1];
+    final d = _distanceToSegment(position, a, b, method: method);
+
+    if (d < distance) {
+      distance = d.toDouble();
+    }
+  });
+
+  return convertLength(distance, Unit.degrees, unit);
+}
+
+/// Returns the distance between a point P on a segment AB.
+num _distanceToSegment(
+  Position p,
+  Position a,
+  Position b, {
+  required DistanceGeometry method,
+}) {
+  final v = b - a;
+  final w = p - a;
+
+  final c1 = w.dotProduct(v);
+  if (c1 <= 0) {
+    return _calcDistance(p, a, method: method, unit: Unit.degrees);
+  }
+
+  final c2 = v.dotProduct(v);
+  if (c2 <= c1) {
+    return _calcDistance(p, b, method: method, unit: Unit.degrees);
+  }
+
+  final b2 = c1 / c2;
+  final pb = a + Position(v[0]! * b2, v[1]! * b2);
+  return _calcDistance(p, pb, method: method, unit: Unit.degrees);
+}
+
+num _calcDistance(
+  Position a,
+  Position b, {
+  required Unit unit,
+  required DistanceGeometry method,
+}) {
+  if (method == DistanceGeometry.planar) {
+    return rhumbDistance(Point(coordinates: a), Point(coordinates: b), unit);
+  }
+
+  // Otherwise DistanceGeometry.geodesic
+  return distanceRaw(a, b, unit);
+}

lib/turf.dart

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

test/components/point_to_line_distance_test.dart

@@ -0,0 +1,96 @@
+import 'dart:convert';
+import 'dart:io';
+
+import 'package:test/test.dart';
+import 'package:turf/helpers.dart';
+import 'package:turf/src/point_to_line_distance.dart';
+
+final distances = {
+  "city-line1.geojson": 1.0299686758,
+  "city-line2.geojson": 3.6186172981,
+  "city-segment-inside1.geojson": 1.1489389115,
+  "city-segment-inside2.geojson": 1.0280898152,
+  "city-segment-inside3.geojson": 3.5335695907,
+  "city-segment-obtuse1.geojson": 2.8573246363,
+  "city-segment-obtuse2.geojson": 3.3538913334,
+  "city-segment-projected1.geojson": 3.5886611693,
+  "city-segment-projected2.geojson": 4.163469898,
+  "issue-1156.geojson": 189.6618028794,
+  "line-fiji.geojson": 27.1266612008,
+  "line-resolute-bay.geojson": 425.0745081528,
+  "line1.geojson": 23.4224834672,
+  "line2.geojson": 188.015686924,
+  "segment-fiji.geojson": 27.6668301762,
+  "segment1.geojson": 69.0934195756,
+  "segment1a.geojson": 69.0934195756,
+  "segment2.geojson": 69.0934195756,
+  "segment3.geojson": 69.0828960461,
+  "segment4.geojson": 332.8803863574
+};
+
+void main() {
+  group('pointToLineDistance', () {
+    group('in == out', () {
+      final inDir = Directory('./test/examples/point_to_line_distance/in');
+
+      for (final file in inDir.listSync(recursive: true)) {
+        if (file is File && file.path.endsWith('.geojson')) {
+          testFile(file);
+        }
+      }
+    });
+
+    group('unit tests', () {
+      testPlanarGeodesic();
+    });
+  });
+}
+
+void testFile(File file) {
+  test(file.path, () {
+    final inSource = file.readAsStringSync();
+    final collection = FeatureCollection.fromJson(jsonDecode(inSource));
+
+    final rawPoint = collection.features[0];
+    final rawLine = collection.features[1];
+
+    final point = Feature<Point>.fromJson(rawPoint.toJson());
+    final line = Feature<LineString>.fromJson(rawLine.toJson());
+
+    final properties = rawPoint.properties ?? {};
+    final unitRaw = properties["units"] as String?;
+
+    var unit = Unit.kilometers;
+    if (unitRaw == 'meters') {
+      unit = Unit.meters;
+    } else if (unitRaw == 'miles') {
+      unit = Unit.miles;
+    } else {
+      expect(unitRaw, null, reason: '"units" was given but not handled.');
+    }
+
+    final distance =
+        pointToLineDistance(point.geometry!, line.geometry!, unit: unit);
+
+    final name = file.path.substring(file.path.lastIndexOf('/') + 1);
+
+    expect(distance, closeTo(distances[name]!, 0.01));
+  });
+}
+
+void testPlanarGeodesic() {
+  test('Check planar and geodesic results are different', () {
+    final pt = Point(coordinates: Position(0, 0));
+    final line = LineString(coordinates: [
+      Position(10, 10),
+      Position(-1, 1),
+    ]);
+
+    final geoOut =
+        pointToLineDistance(pt, line, method: DistanceGeometry.geodesic);
+    final planarOut =
+        pointToLineDistance(pt, line, method: DistanceGeometry.planar);
+
+    expect(geoOut, isNot(equals(planarOut)));
+  });
+}

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

@@ -0,0 +1,30 @@
+{
+  "type": "FeatureCollection",
+  "features": [
+    {
+      "type": "Feature",
+      "properties": {},
+      "geometry": {
+        "type": "Point",
+        "coordinates": [-0.3767967224121093, 39.4689324766527]
+      }
+    },
+    {
+      "type": "Feature",
+      "properties": {},
+      "geometry": {
+        "type": "LineString",
+        "coordinates": [
+          [-0.40567874908447266, 39.47386857192064],
+          [-0.3963661193847656, 39.47578991028725],
+          [-0.38035869598388666, 39.482216070269594],
+          [-0.3776121139526367, 39.48195108571802],
+          [-0.3689002990722656, 39.47641930269614],
+          [-0.35945892333984375, 39.46349905420083],
+          [-0.35782814025878906, 39.45982131412374],
+          [-0.3458118438720703, 39.453890134716616]
+        ]
+      }
+    }
+  ]
+}

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

@@ -0,0 +1,27 @@
+{
+  "type": "FeatureCollection",
+  "features": [
+    {
+      "type": "Feature",
+      "properties": {},
+      "geometry": {
+        "type": "Point",
+        "coordinates": [-3.592529296875, 40.573804799488194]
+      }
+    },
+    {
+      "type": "Feature",
+      "properties": {},
+      "geometry": {
+        "type": "LineString",
+        "coordinates": [
+          [-3.8884735107421875, 40.420292132688964],
+          [-3.736724853515625, 40.276906410822825],
+          [-3.5025787353515625, 40.422383097039905],
+          [-3.5018920898437496, 40.516409213865586],
+          [-3.668060302734375, 40.559199680578075]
+        ]
+      }
+    }
+  ]
+}

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

@@ -0,0 +1,26 @@
+{
+  "type": "FeatureCollection",
+  "features": [
+    {
+      "type": "Feature",
+      "properties": {
+        "units": "miles"
+      },
+      "geometry": {
+        "type": "Point",
+        "coordinates": [-6.0047149658203125, 37.365109304227246]
+      }
+    },
+    {
+      "type": "Feature",
+      "properties": {},
+      "geometry": {
+        "type": "LineString",
+        "coordinates": [
+          [-6.0150146484375, 37.38011551844836],
+          [-5.931415557861328, 37.39702801486944]
+        ]
+      }
+    }
+  ]
+}

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

@@ -0,0 +1,24 @@
+{
+  "type": "FeatureCollection",
+  "features": [
+    {
+      "type": "Feature",
+      "properties": {},
+      "geometry": {
+        "type": "Point",
+        "coordinates": [-0.3767967224121093, 39.4689324766527]
+      }
+    },
+    {
+      "type": "Feature",
+      "properties": {},
+      "geometry": {
+        "type": "LineString",
+        "coordinates": [
+          [-0.3689861297607422, 39.47648555419739],
+          [-0.3595447540283203, 39.46363158174706]
+        ]
+      }
+    }
+  ]
+}

test/examples/point_to_line_distance/in/city-segment-inside3.geojson

@@ -0,0 +1,24 @@
+{
+  "type": "FeatureCollection",
+  "features": [
+    {
+      "type": "Feature",
+      "properties": {},
+      "geometry": {
+        "type": "Point",
+        "coordinates": [-3.592529296875, 40.573804799488194]
+      }
+    },
+    {
+      "type": "Feature",
+      "properties": {},
+      "geometry": {
+        "type": "LineString",
+        "coordinates": [
+          [-3.503265380859375, 40.51693121343741],
+          [-3.6694335937500004, 40.560764667193595]
+        ]
+      }
+    }
+  ]
+}

test/examples/point_to_line_distance/in/city-segment-obtuse1.geojson

@@ -0,0 +1,24 @@
+{
+  "type": "FeatureCollection",
+  "features": [
+    {
+      "type": "Feature",
+      "properties": {},
+      "geometry": {
+        "type": "Point",
+        "coordinates": [-6.030292510986328, 37.35746862390723]
+      }
+    },
+    {
+      "type": "Feature",
+      "properties": {},
+      "geometry": {
+        "type": "LineString",
+        "coordinates": [
+          [-6.0150146484375, 37.38011551844836],
+          [-5.931415557861328, 37.39702801486944]
+        ]
+      }
+    }
+  ]
+}