实现map上车辆移动时，车图方向总是指向移动方向

类似功能如图
思想：从java端利用相邻两个点的经纬度，算出旋转角；然后，用Arcgis API设置旋转角。此处注意不要在前端计算旋转角，在java端性能会更好。

计算旋转角


            if(cityName.equals("SZ") && i+1 < list.size() && firstLat != null && firstLon != null){

                double[] offSetDateFist = GpsUtil.toGCJ02Point(Double.parseDouble(String.valueOf(list.get(i)[5])),Double.parseDouble(String.valueOf(list.get(i)[4])));
                double[] offSetDateNext = GpsUtil.toGCJ02Point(Double.parseDouble(String.valueOf(list.get(i+1)[5])),Double.parseDouble(String.valueOf(list.get(i+1)[4])));

                Double firstOffSetLon = offSetDateFist[1];
                Double firstOffSetLat = offSetDateFist[0];
                Double nextOffSetLon = offSetDateNext[1];
                Double nextOffSetLat = offSetDateNext[0];

                double xgap = firstOffSetLon - nextOffSetLon;
                double ygap = firstOffSetLat - nextOffSetLat;

                double dou;
                double dou1;
                dou = Math.abs(xgap);
                dou1 = Math.abs(ygap);

                DecimalFormat df = new DecimalFormat("#.00000");

                if(Double.parseDouble( df.format(dou)) > 0.00001 && Double.parseDouble( df.format(dou1)) >0.00001){
                    double angle = GpsUtil.getAngle(firstOffSetLon,firstOffSetLat,nextOffSetLon,nextOffSetLat);
//                        double angle = GpsUtil.getAngle(firstOffSetLat,firstOffSetLon,nextOffSetLat ,nextOffSetLon);
                    map.put("angle",String.valueOf(angle));
                }
            }


2. 计算旋转角的方法getAngle

public static double getAngle(double firstLon,double firstLat,double nextLon,double nextLat){
    double dRotateAngle = Math.atan2(Math.abs(firstLon - nextLon), Math.abs(firstLat - nextLat));
    if (nextLon >= firstLon) {
        if (nextLat >= firstLat) {
        } else {
            dRotateAngle = Math.PI - dRotateAngle;
        }
    } else {
        if (nextLat >= firstLat) {
            dRotateAngle = 2 * Math.PI - dRotateAngle;
        } else {
            dRotateAngle = Math.PI + dRotateAngle;
        }
    }
    dRotateAngle = dRotateAngle * 180 / Math.PI;
    return dRotateAngle;
}



3. 前端实现
`var symbolw =new esri.symbol.PictureMarkerSymbol(mapConfig.testDirection,mapConfig.playWaveSize, mapConfig.playWaveSize);` PictureMarkerSymbol有个设置旋转角的方法`symbolw.setAngle(app.angleData[playi]);`

cccreator / GIS

实现map上车辆移动时，车图方向总是指向移动方向 #7