使用 Yandex Map 和 flutter_map package 时位置 lat-lng 出错

Question

我正在使用flutter_map和yandex map，如下所示。 当我标记一个位置时，获取位置 lat 和 lon 是错误的。 所以如果我在 map 上画一个多边形，它画在错误的位置。 如何解决这个问题？

 FlutterMap(
  options: MapOptions(
    center: LatLng(41.334554,36.269617),
    zoom: 11.0,
    maxZoom: 18,
    minZoom: 5,
    plugins: [
      DragMarkerPlugin(),
    ],
    onTap: (value){
      print(value.toString());
      markLocation(value);
    },
  ),
  layers: [
    TileLayerOptions(
        urlTemplate: 'https://core-sat.maps.yandex.net/tiles?l=sat&v=3.569.0&x={x}&y={y}&z={z}&lang=tr_TR'
    ),
    TileLayerOptions(
        urlTemplate: 'http://vec{s}.maps.yandex.net/tiles?l=skl&v=20.06.03&z={z}&x={x}&y={y}&scale=1&lang=tr_TR',
        subdomains: ['01', '02', '03', '04'],
        backgroundColor: Colors.transparent
    ),
    CircleLayerOptions(
        circles: _circles
    ),
    PolygonLayerOptions(
      polygons: getPolygons()
    ),
    DragMarkerPluginOptions(
      markers: _markers
    )
  ],
  mapController: _mapController,
)

多边形的实际 position：

以及如何在设备上查看？

Answer 1

我使用自定义 csr 来解决这个问题。 感谢 dmitrienkop 的回答。

https://github.com/fleaflet/flutter_map/issues/642

import 'dart:math' as math;
import 'package:flutter_map/plugin_api.dart';
import 'package:latlong/latlong.dart';

class Epsg3395 extends Earth {
  @override
  final String code = 'EPSG:3395';

  @override
  final Projection projection = const Mercator();

  @override
  final Transformation transformation = const Transformation(_scale, 0.5, -_scale, 0.5);

  static const num _scale = 0.5 / (math.pi * Mercator.r);

  const Epsg3395() : super();
}

class Mercator extends Projection {
  static const int r = 6378137;
  static const double rMinor = 6356752.314245179;
  static final Bounds<double> _bounds = Bounds<double>(
    CustomPoint<double>(-20037508.34279, -15496570.73972),
    CustomPoint<double>(20037508.34279, 18764656.23138),
  );

  const Mercator() : super();

  @override
  Bounds<double> get bounds => _bounds;

  @override
  CustomPoint project(LatLng latlng) {
    var d = math.pi / 180;
    var y = latlng.latitude * d;
    var tmp = rMinor / r;
    var e = math.sqrt(1 - tmp * tmp);
    var con = e * math.sin(y);

    var ts = math.tan(math.pi / 4 - y / 2) / math.pow((1 - con) / (1 + con), e / 2);
    y = -r * math.log(math.max(ts, 1E-10));

    return CustomPoint(latlng.longitude * d * r, y);
  }

  @override
  LatLng unproject(CustomPoint point) {
    var d = 180 / math.pi;
    var tmp = rMinor / r;
    var e = math.sqrt(1 - tmp * tmp);
    var ts = math.exp(-point.y / r);
    var phi = math.pi / 2 - 2 * math.atan(ts);

    for (var i = 0, dphi = 0.1, con; i < 15 && dphi.abs() > 1e-7; i++) {
            con = e * math.sin(phi);
            con = math.pow((1 - con) / (1 + con), e / 2);
            dphi = math.pi / 2 - 2 * math.atan(ts * con) - phi;
            phi += dphi;
        }

    return LatLng(phi * d, point.x * d / r);
  }
}