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Add: simplify for Feature<LineString>, ported from turf.js (#183)
* Add: simplify for Feature<LineString>, ported from turf.js * Doc: update Progress.md
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‎Progress.md‎

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@@ -49,7 +49,7 @@ Dart. This is an on going project and functions are being added once needed. If
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- [ ] intersect
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- [ ] lineOffset
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- [x] [polygonSmooth](https://github.com/dartclub/turf_dart/blob/main/lib/src/polygon_smooth.dart)
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- [ ] simplify
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- [x] [simplify](https://github.com/dartclub/turf_dart/blob/main/lib/src/simplify.dart)
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- [ ] tesselate
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- [x] [transformRotate](https://github.com/dartclub/turf_dart/blob/main/lib/src/transform_rotate.dart)
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- [ ] transformTranslate

‎lib/simplify.dart‎

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library turf_simplify;
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export 'package:geotypes/geotypes.dart';
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export 'src/simplify.dart';

‎lib/src/simplify.dart‎

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import 'package:turf/helpers.dart';
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import 'package:turf/turf.dart';
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/*
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(c) 2013, Vladimir Agafonkin
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Simplify.js, a high-performance JS polyline simplification library
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mourner.github.io/simplify-js
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*/
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// to suit your point format, run search/replace for '.x' and '.y';
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// for 3D version, see 3d branch (configurability would draw significant performance overhead)
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/// square distance between 2 points
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num _getSqDist(Position p1, Position p2) {
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var dx = p1.lng - p2.lng, dy = p1.lat - p2.lat;
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return dx * dx + dy * dy;
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}
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/// square distance from a point to a segment
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num _getSqSegDist(Position p, Position p1, Position p2) {
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var x = p1.lng, y = p1.lat, dx = p2.lng - x, dy = p2.lat - y;
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if (dx != 0 || dy != 0) {
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var t = ((p.lng - x) * dx + (p.lat - y) * dy) / (dx * dx + dy * dy);
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if (t > 1) {
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x = p2.lng;
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y = p2.lat;
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} else if (t > 0) {
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x += dx * t;
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y += dy * t;
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}
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}
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dx = p.lng - x;
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dy = p.lat - y;
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return dx * dx + dy * dy;
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}
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// rest of the code doesn't care about point format
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/// basic distance-based simplification
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List<Position> _simplifyRadialDist(List<Position> points, double sqTolerance) {
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var prevPoint = points[0], newPoints = [prevPoint];
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late Position point;
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for (var i = 1, len = points.length; i < len; i++) {
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point = points[i];
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if (_getSqDist(point, prevPoint) > sqTolerance) {
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newPoints.add(point);
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prevPoint = point;
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}
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}
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if (prevPoint != point) newPoints.add(point);
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return newPoints;
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}
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List<Position> _simplifyDPStep(List<Position> points, int first, int last,
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double sqTolerance, List<Position> simplified) {
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num maxSqDist = sqTolerance;
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late int index;
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for (var i = first + 1; i < last; i++) {
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var sqDist = _getSqSegDist(points[i], points[first], points[last]);
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if (sqDist > maxSqDist) {
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index = i;
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maxSqDist = sqDist;
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}
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}
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if (maxSqDist > sqTolerance) {
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if (index - first > 1) {
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simplified =
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_simplifyDPStep(points, first, index, sqTolerance, simplified);
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}
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simplified.add(points[index]);
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if (last - index > 1) {
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simplified =
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_simplifyDPStep(points, index, last, sqTolerance, simplified);
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}
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}
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return simplified;
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}
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/// simplification using Ramer-Douglas-Peucker algorithm
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List<Position> _simplifyDouglasPeucker(List<Position> points, sqTolerance) {
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final last = points.length - 1;
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var simplified = [points[0]];
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simplified = _simplifyDPStep(points, 0, last, sqTolerance, simplified);
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simplified.add(points[last]);
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return simplified;
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}
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/// Simplify a LineString feature using dart port of simplify.js high-performance JS polyline simplification library.
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///
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/// both algorithms combined for awesome performance
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Feature<LineString> simplify(
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Feature<LineString> points, {
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double tolerance = 1,
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bool highestQuality = false,
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}) {
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var coords = getCoords(points);
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if (coords.length <= 2) return points;
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if (coords is! List<Position>) return points;
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final sqTolerance = tolerance * tolerance;
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coords = highestQuality ? coords : _simplifyRadialDist(coords, sqTolerance);
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coords = _simplifyDouglasPeucker(coords, sqTolerance);
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return Feature<LineString>(
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id: points.id,
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geometry: LineString(coordinates: coords),
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properties: points.properties,
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bbox: points.bbox,
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);
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}

‎test/components/simplify_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/along.dart';
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import 'package:turf/area.dart';
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import 'package:turf/simplify.dart';
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main() {
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group(
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'simplify in == out',
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() {
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var inDir = Directory('./test/examples/simplify/in');
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for (var file in inDir.listSync(recursive: true)) {
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if (file is File && file.path.endsWith('.geojson')) {
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test(
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file.path,
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() {
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var inSource = file.readAsStringSync();
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var inGeom = Feature<LineString>.fromJson(jsonDecode(inSource));
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var inSimplified = simplify(
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inGeom,
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tolerance: inGeom.properties?['tolerance'] ?? 0.01,
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highestQuality: inGeom.properties?['highQuality'] ?? false,
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);
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// ignore: prefer_interpolation_to_compose_strings
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var outPath = './' +
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file.uri.pathSegments
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.sublist(0, file.uri.pathSegments.length - 2)
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.join('/') +
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'/out/${file.uri.pathSegments.last}';
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var outSource = File(outPath).readAsStringSync();
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var outGeom = Feature<LineString>.fromJson(jsonDecode(outSource));
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final precision = 0.0001;
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expect(inSimplified.id, outGeom.id);
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expect(inSimplified.properties, equals(outGeom.properties));
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expect(inSimplified.geometry, isNotNull);
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expect(
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_roundCoords(inSimplified.geometry!.coordinates, precision),
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_roundCoords(outGeom.geometry!.coordinates, precision));
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},
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);
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}
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}
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},
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);
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test(
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'simplify retains id, properties and bbox',
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() {
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const properties = {"foo": "bar"};
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const id = 12345;
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final bbox = BBox(0, 0, 2, 2);
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final poly = Feature<LineString>(
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geometry: LineString(coordinates: [
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Position(0, 0),
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Position(2, 2),
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Position(2, 0),
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Position(0, 0),
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]),
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properties: properties,
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bbox: bbox,
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id: id,
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);
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final simple = simplify(poly, tolerance: 0.1);
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expect(simple.id, equals(id));
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expect(simple.bbox, equals(bbox));
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expect(simple.properties, equals(properties));
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},
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);
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}
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List<Position> _roundCoords(List<Position> coords, num precision) {
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return coords
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.map((p) => Position(_round(p.lng, precision), _round(p.lat, precision)))
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.toList();
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}
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num _round(num value, num precision) {
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return (value / precision).roundToDouble() * precision;
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}

‎test/examples/simplify/in/linestring.geojson‎

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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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[-80.51399230957031, 28.069556808283608],
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[-80.51193237304688, 28.057438520876673],
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[-80.49819946289062, 28.05622661698537],
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[-80.5023193359375, 28.04471284867091],
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[-80.48583984375, 28.042288740362853],
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[-80.50575256347656, 28.028349057505775],
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[-80.50163269042969, 28.02168161433489],
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[-80.49476623535156, 28.021075462659883],
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[-80.48652648925781, 28.021075462659883],
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[-80.47691345214844, 28.021075462659883],
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[-80.46936035156249, 28.015619944017807],
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[-80.47760009765624, 28.007133032319448],
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[-80.49201965332031, 27.998039170620494],
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[-80.46730041503906, 27.962262536875905],
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[-80.46524047851562, 27.91980029694533],
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[-80.40550231933594, 27.930114089618602],
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[-80.39657592773438, 27.980455528671527],
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[-80.41305541992188, 27.982274659104082],
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[-80.42953491210938, 27.990763528690582],
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[-80.4144287109375, 28.00955793247135],
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[-80.3594970703125, 27.972572275562527],
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[-80.36224365234375, 27.948919060105453],
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[-80.38215637207031, 27.913732900444284],
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[-80.41786193847656, 27.881570017022806],
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[-80.40550231933594, 27.860932192608534],
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[-80.39382934570312, 27.85425440786446],
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[-80.37803649902344, 27.86336037597851],
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[-80.38215637207031, 27.880963078302393],
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[-80.36842346191405, 27.888246118437756],
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[-80.35743713378906, 27.882176952341734],
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[-80.35469055175781, 27.86882358965466],
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[-80.3594970703125, 27.8421119273228],
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[-80.37940979003906, 27.83300417483936],
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[-80.39932250976561, 27.82511017099003],
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[-80.40069580078125, 27.79352841586229],
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[-80.36155700683594, 27.786846483587688],
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[-80.35537719726562, 27.794743268514615],
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[-80.36705017089844, 27.800209937418252],
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[-80.36889553070068, 27.801918215058347],
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[-80.3690242767334, 27.803930152059845],
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[-80.36713600158691, 27.805942051806845],
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[-80.36584854125977, 27.805524490772143],
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[-80.36563396453857, 27.80465140342285],
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[-80.36619186401367, 27.803095012921272],
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[-80.36623477935791, 27.801842292177923],
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[-80.36524772644043, 27.80127286888392],
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[-80.36224365234375, 27.801158983867033],
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[-80.36065578460693, 27.802639479776524],
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[-80.36138534545898, 27.803740348273823],
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[-80.36220073699951, 27.804803245204976],
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[-80.36190032958984, 27.806625330038287],
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[-80.3609561920166, 27.80742248254359],
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[-80.35932540893555, 27.806853088493792],
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[-80.35889625549315, 27.806321651354835],
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[-80.35902500152588, 27.805448570411585],
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[-80.35863876342773, 27.804461600896783],
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[-80.35739421844482, 27.804461600896783],
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[-80.35700798034668, 27.805334689771293],
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[-80.35696506500244, 27.80673920932572],
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[-80.35726547241211, 27.80772615814989],
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[-80.35808086395264, 27.808295547623707],
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[-80.3585958480835, 27.80928248230861],
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[-80.35653591156006, 27.80943431761813],
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[-80.35572052001953, 27.808637179875486],
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[-80.3555917739868, 27.80772615814989],
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[-80.3555917739868, 27.806055931810487],
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[-80.35572052001953, 27.803778309057556],
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[-80.35537719726562, 27.801804330717825],
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[-80.3554630279541, 27.799564581098746],
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[-80.35670757293701, 27.799564581098746],
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[-80.35499095916748, 27.796831264786892],
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[-80.34610748291016, 27.79478123244122],
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[-80.34404754638672, 27.802070060660014],
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[-80.34748077392578, 27.804955086774896],
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[-80.3433609008789, 27.805790211616266],
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[-80.34353256225586, 27.8101555324401],
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[-80.33499240875244, 27.810079615315917],
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[-80.33383369445801, 27.805676331334084],
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[-80.33022880554199, 27.801652484744796],
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[-80.32872676849365, 27.80848534345178]
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]
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}
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}

‎test/examples/simplify/out/linestring.geojson‎

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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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[-80.513992, 28.069557],
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[-80.48584, 28.042289],
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[-80.505753, 28.028349],
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[-80.476913, 28.021075],
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[-80.49202, 27.998039],
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[-80.4673, 27.962263],
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[-80.46524, 27.9198],
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[-80.405502, 27.930114],
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[-80.396576, 27.980456],
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[-80.429535, 27.990764],
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[-80.414429, 28.009558],
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[-80.359497, 27.972572],
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[-80.382156, 27.913733],
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[-80.417862, 27.88157],
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[-80.393829, 27.854254],
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[-80.368423, 27.888246],
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[-80.354691, 27.868824],
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[-80.359497, 27.842112],
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[-80.399323, 27.82511],
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[-80.400696, 27.793528],
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[-80.361557, 27.786846],
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[-80.359325, 27.806853],
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[-80.354991, 27.796831],
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[-80.328727, 27.808485]
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]
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}
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}

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