Terepbejárás: geometriák hosszának és területének számítása és jelzése

lib/core/geometry_measure.dart

@@ -0,0 +1,105 @@
+import 'dart:math';
+
+import 'package:latlong2/latlong.dart';
+
+class GeometryMeasure {
+  static final Distance _distance = const Distance();
+
+  static double lineLengthMeters(List<LatLng> points) {
+    if (points.length < 2) return 0.0;
+
+    double sum = 0.0;
+
+    for (var i = 1; i < points.length; i++) {
+      sum += _distance.as(
+        LengthUnit.Meter,
+        points[i - 1],
+        points[i],
+      );
+    }
+
+    return sum;
+  }
+
+  static double polygonAreaSquareMeters(List<LatLng> points) {
+    final polygon = _normalizedPolygon(points);
+
+    if (polygon.length < 3) return 0.0;
+
+    final origin = _centroid(polygon);
+    final projected =
+        polygon.map((p) => _projectToLocalMeters(p, origin)).toList();
+
+    double area = 0.0;
+
+    for (var i = 0; i < projected.length; i++) {
+      final j = (i + 1) % projected.length;
+
+      area += projected[i].x * projected[j].y - projected[j].x * projected[i].y;
+    }
+
+    return area.abs() / 2.0;
+  }
+
+  static List<LatLng> _normalizedPolygon(List<LatLng> source) {
+    final points = List<LatLng>.from(source);
+
+    if (points.length < 2) return points;
+
+    final first = points.first;
+    final last = points.last;
+
+    final closeDistance = _distance.as(
+      LengthUnit.Meter,
+      first,
+      last,
+    );
+
+    if (closeDistance < 0.01) {
+      points.removeLast();
+    }
+
+    return points;
+  }
+
+  static LatLng _centroid(List<LatLng> points) {
+    double lat = 0.0;
+    double lon = 0.0;
+
+    for (final p in points) {
+      lat += p.latitude;
+      lon += p.longitude;
+    }
+
+    return LatLng(
+      lat / points.length,
+      lon / points.length,
+    );
+  }
+
+  static _Point2D _projectToLocalMeters(
+    LatLng point,
+    LatLng origin,
+  ) {
+    const earthRadius = 6378137.0;
+
+    final latRad = point.latitude * pi / 180.0;
+    final lonRad = point.longitude * pi / 180.0;
+
+    final originLatRad = origin.latitude * pi / 180.0;
+    final originLonRad = origin.longitude * pi / 180.0;
+
+    final x = earthRadius * (lonRad - originLonRad) * cos(originLatRad);
+
+    final y = earthRadius * (latRad - originLatRad);
+
+    return _Point2D(x, y);
+  }
+}
+
+class _Point2D {
+  final double x;
+  final double y;
+
+  const _Point2D(this.x, this.y);
+}