问题描述

我正在创建一个 Android 应用程序，它需要在 X 公里后在同一条路线上找到一个坐标.

I am creating an Android app which requires finding a coordinate on the same route after X kilometers.

我有两个坐标 x1,y1 &x2,y2 在路上.现在，我的要求是在大约 3 公里后找到坐标 x3,y3 (即，在 x2,y2 之后的坐标不在 x1,y1 和; x2,y2) 在同一条路上.

I have two coordinates x1,y1 & x2,y2 on a road. Now, my requirement is to find coordinate x3,y3 after some 3 kilometers (i.e., coordinate after x2,y2 not between x1,y1 & x2,y2) on the same road.

如何做到这一点?

推荐答案

如果你知道 轴承，可以计算出目的地坐标.

If you know the bearing, you can calculate the destination coordinate.

示例代码:

private LatLng getDestinationPoint(LatLng source, double brng, double dist) {
        dist = dist / 6371;
        brng = Math.toRadians(brng);

        double lat1 = Math.toRadians(source.latitude), lon1 = Math.toRadians(source.longitude);
        double lat2 = Math.asin(Math.sin(lat1) * Math.cos(dist) +
                                Math.cos(lat1) * Math.sin(dist) * Math.cos(brng));
        double lon2 = lon1 + Math.atan2(Math.sin(brng) * Math.sin(dist) *
                                        Math.cos(lat1),
                                        Math.cos(dist) - Math.sin(lat1) *
                                        Math.sin(lat2));
        if (Double.isNaN(lat2) || Double.isNaN(lon2)) {
            return null;
        }
        return new LatLng(Math.toDegrees(lat2), Math.toDegrees(lon2));
    }

示例用法:

   double radiusInKM = 10.0;
   double bearing = 90;
   LatLng destinationPoint = getDestinationPoint(new LatLng((25.48, -71.26), bearing, radiusInKM);

或者您可以在 pointA 和 pointB 之间使用航向而不是方位:

Or you can use heading between your pointA and pointB instead of bearing:

LatLng destinationPoint = getDestinationPoint(new LatLng(37.4038194,-122.081267), SphericalUtil.computeHeading(new LatLng(37.7577,-122.4376), new LatLng(37.4038194,-122.081267)), radiusInKM);

SphericalUtil.computeHeading(p1, p2); 方法来自 Android Google 地图实用程序库.

这是基于 this Stackoverflow answer 中的 Javascript 方法.

This is based on the Javascript method from this Stackoverflow answer.

如果您想在同一条道路上找到该点，您可以查看此 PHP 答案.

If you want the point on same road, you might checkout this PHP answer.

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