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implementation of polyline and polygon simplification
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| Original file line number | Diff line number | Diff line change |
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| // implementation based on | ||
| // https://github.com/mourner/simplify-js/blob/master/simplify.js | ||
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| import 'package:latlong2/latlong.dart'; | ||
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| double _getSqDist( | ||
| LatLng p1, | ||
| LatLng p2, | ||
| ) { | ||
| final double dx = p1.longitude - p2.longitude; | ||
| final double dy = p1.latitude - p2.latitude; | ||
| return dx * dx + dy * dy; | ||
| } | ||
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| // square distance from a point to a segment | ||
| double _getSqSegDist( | ||
| LatLng p, | ||
| LatLng p1, | ||
| LatLng p2, | ||
| ) { | ||
| double x = p1.longitude; | ||
| double y = p1.latitude; | ||
| double dx = p2.longitude - x; | ||
| double dy = p2.latitude - y; | ||
| if (dx != 0 || dy != 0) { | ||
| final double t = | ||
| ((p.longitude - x) * dx + (p.latitude - y) * dy) / | ||
| (dx * dx + dy * dy); | ||
| if (t > 1) { | ||
| x = p2.longitude; | ||
| y = p2.latitude; | ||
| } else if (t > 0) { | ||
| x += dx * t; | ||
| y += dy * t; | ||
| } | ||
| } | ||
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| dx = p.longitude - x; | ||
| dy = p.latitude - y; | ||
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| return dx * dx + dy * dy; | ||
| } | ||
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| List<LatLng> _simplifyRadialDist( | ||
| List<LatLng> points, | ||
| double sqTolerance, | ||
| ) { | ||
| LatLng prevPoint = points[0]; | ||
| final List<LatLng> newPoints = [prevPoint]; | ||
| late LatLng point; | ||
| for (int i = 1, len = points.length; i < len; i++) { | ||
| point = points[i]; | ||
| if (_getSqDist(point, prevPoint) > sqTolerance) { | ||
| newPoints.add(point); | ||
| prevPoint = point; | ||
| } | ||
| } | ||
| if (prevPoint != point) { | ||
| newPoints.add(point); | ||
| } | ||
| return newPoints; | ||
| } | ||
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| void _simplifyDPStep( | ||
| List<LatLng> points, | ||
| int first, | ||
| int last, | ||
| double sqTolerance, | ||
| List<LatLng> simplified, | ||
| ) { | ||
| double maxSqDist = sqTolerance; | ||
| late int index; | ||
| for (int i = first + 1; i < last; i++) { | ||
| final double sqDist = _getSqSegDist(points[i], points[first], points[last]); | ||
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| if (sqDist > maxSqDist) { | ||
| index = i; | ||
| maxSqDist = sqDist; | ||
| } | ||
| } | ||
| if (maxSqDist > sqTolerance) { | ||
| if (index - first > 1) { | ||
| _simplifyDPStep(points, first, index, sqTolerance, simplified); | ||
| } | ||
| simplified.add(points[index]); | ||
| if (last - index > 1) { | ||
| _simplifyDPStep(points, index, last, sqTolerance, simplified); | ||
| } | ||
| } | ||
| } | ||
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| // simplification using Ramer-Douglas-Peucker algorithm | ||
| List<LatLng> _simplifyDouglasPeucker( | ||
| List<LatLng> points, | ||
| double sqTolerance, | ||
| ) { | ||
| final int last = points.length - 1; | ||
| final List<LatLng> simplified = [points[0]]; | ||
| _simplifyDPStep(points, 0, last, sqTolerance, simplified); | ||
| simplified.add(points[last]); | ||
| return simplified; | ||
| } | ||
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| // both algorithms combined for awesome performance | ||
| List<LatLng> simplify( | ||
| List<LatLng> points, | ||
| double tolerance, { | ||
| bool highestQuality = false, | ||
| }) { | ||
| if (points.length <= 2) { | ||
| return points; | ||
| } | ||
| List<LatLng> nextPoints = points; | ||
| final double sqTolerance = tolerance * tolerance; | ||
| nextPoints = | ||
| highestQuality ? points : _simplifyRadialDist(nextPoints, sqTolerance); | ||
| nextPoints = _simplifyDouglasPeucker(nextPoints, sqTolerance); | ||
| return nextPoints; | ||
| } |