android  map  （google map ,百度 ，高德 ）在路線 上畫箭頭！

其實分為2步驟： 算角度，畫箭頭marker ,marker 畫在路線兩個點的中點

public void drawArrow(List<LatLng> list) {
    LogUtils.show(TAG, "開始畫箭頭");
    if (list == null || list.size() <= 1) {
        LogUtils.show(TAG, "開始畫箭頭------失敗");
        return;
}
    LogUtils.show(TAG
 
, "開始畫箭頭------失滿足條件");
    for (int i = 1; i < list.size(); i++) {
        double lat1 = list.get(i - 1).latitude;
        double lng1 = list.get(i - 1).longitude;
        double lat2 = list.get(i).latitude;
        double lng2 = list.get(i).longitude;
        double lat = (lat1 + lat2) / 2;
        double 
 
lng = (lng1 + lng2) / 2;
LatLng modLat = new LatLng(lat, lng);
        double brng = computeAzimuth(new LatLng(lat1, lng1), new LatLng(lat2, lng2));
MarkerOptions marker = new MarkerOptions().position(modLat);
marker.anchor(0.5f, 0.5f);
marker.icon(BitmapDescriptorFactory.fromResource(R.mipmap.line_arrow
 
));
marker.rotation((float) brng);
marker.flat(true);
mMap.addMarker(marker);
LogUtils.show(TAG, "開始畫箭頭------箭頭-- " + i + "角度為  " + brng);
}

}


// 計算方位角,正北向為0度，以順時針方向遞增
private double computeAzimuth(LatLng la1, LatLng la2) {
    double lat1 = la1.latitude, lon1 = la1.longitude, lat2 = la2.latitude,
lon2 = la2.longitude;
    double result = 0.0;
    int ilat1 = (int) (0.50 + lat1 * 360000.0);
    int ilat2 = (int) (0.50 + lat2 * 360000.0);
    int ilon1 = (int) (0.50 + lon1 * 360000.0);
    int ilon2 = (int) (0.50 + lon2 * 360000.0);
lat1 = Math.toRadians(lat1);
lon1 = Math.toRadians(lon1);
lat2 = Math.toRadians(lat2);
lon2 = Math.toRadians(lon2);
    if ((ilat1 == ilat2) && (ilon1 == ilon2)) {
        return result;
} else if (ilon1 == ilon2) {
        if (ilat1 > ilat2)
            result = 180.0;
} else {
        double c = Math
                .acos(Math.sin(lat2) * Math.sin(lat1) + Math.cos(lat2)
                        * Math.cos(lat1) * Math.cos((lon2 - lon1)));
        double A = Math.asin(Math.cos(lat2) * Math.sin((lon2 - lon1))
                / Math.sin(c));
result = Math.toDegrees(A);
        if ((ilat2 > ilat1) && (ilon2 > ilon1)) {
        } else if ((ilat2 < ilat1) && (ilon2 < ilon1)) {
            result = 180.0 - result;
} else if ((ilat2 < ilat1) && (ilon2 > ilon1)) {
            result = 180.0 - result;
} else if ((ilat2 > ilat1) && (ilon2 < ilon1)) {
            result += 360.0;
}
    }
    return result;
}