使用Google Directions API地图查看绘制路线 - 解码折线

Question

我正在尝试使用Google Directions API在我的mapview上显示路线,但我很难从JSON响应中获取数据.我可以获得"级别"和"点"字符串,但无法解决如何将它们解码到地图上的点.

任何帮助将非常感激.

Answer 1

我有一个类可以为你解码它们,添加下面的类然后在你的代码中调用如下:

int[] decodedZoomLevels = PolylineDecoder.decodeZoomLevels(levels);
GeoPoint[] gPts = PolylineDecoder.decodePoints(points, decodedZoomLevels.length);

您从JSON响应中提取的数据的位置points和levels位置.然后,您可以浏览一系列地理点,在它们之间画一条线来显示您的路线.

希望这可以帮助!肯尼

编辑:似乎谷歌方向API不再返回缩放级别字符串作为JSON响应的一部分,不过不用担心,我们所使用的只是检查点数,所以我们可以简单地将这些列表如:

public static List <GeoPoint> decodePoints(String encoded_points){
int index = 0;
int lat = 0;
int lng = 0;
List <GeoPoint> out = new ArrayList<GeoPoint>();

try {
    int shift;
    int result;
    while (index < encoded_points.length()) {
        shift = 0;
        result = 0;
        while (true) {
            int b = encoded_points.charAt(index++) - '?';
            result |= ((b & 31) << shift);
            shift += 5;
            if (b < 32)
                break;
        }
        lat += ((result & 1) != 0 ? ~(result >> 1) : result >> 1);

        shift = 0;
        result = 0;
        while (true) {
            int b = encoded_points.charAt(index++) - '?';
            result |= ((b & 31) << shift);
            shift += 5;
            if (b < 32)
                break;
        }
        lng += ((result & 1) != 0 ? ~(result >> 1) : result >> 1);
        /* Add the new Lat/Lng to the Array. */
        out.add(new GeoPoint((lat*10),(lng*10)));
    }
    return out;
}catch(Exception e) {
    e.printStackTrace();
}
return out;
}

编辑:旧代码

public class PolylineDecoder {
/**
 * Transform a encoded PolyLine to a Array of GeoPoints.
 * Java implementation of the original Google JS code.
 * @see Original encoding part: <a href="http://code.google.com/apis/maps/documentation/polylinealgorithm.html">http://code.google.com/apis/maps/documentation/polylinealgorithm.html</a>
 * @return Array of all GeoPoints decoded from the PolyLine-String.
 * @param encoded_points String containing the encoded PolyLine. 
 * @param countExpected Number of points that are encoded in the PolyLine. Easiest way is to use the length of the ZoomLevels-String. 
 * @throws DecodingException 
 */
public static GeoPoint[] decodePoints(String encoded_points, int countExpected){
    int index = 0;
    int lat = 0;
    int lng = 0;
    int cnt = 0;
    GeoPoint[] out = new GeoPoint[countExpected];

    try {
        int shift;
        int result;
        while (index < encoded_points.length()) {
            shift = 0;
            result = 0;
            while (true) {
                int b = encoded_points.charAt(index++) - '?';
                result |= ((b & 31) << shift);
                shift += 5;
                if (b < 32)
                    break;
            }
            lat += ((result & 1) != 0 ? ~(result >> 1) : result >> 1);

            shift = 0;
            result = 0;
            while (true) {
                int b = encoded_points.charAt(index++) - '?';
                result |= ((b & 31) << shift);
                shift += 5;
                if (b < 32)
                    break;
            }
            lng += ((result & 1) != 0 ? ~(result >> 1) : result >> 1);
            /* Add the new Lat/Lng to the Array. */
            out[cnt++] = new GeoPoint((lat*10),(lng*10));
        }
        return out;
    }catch(Exception e) {
        e.printStackTrace();
    }
    return out;
}

public static int[] decodeZoomLevels(String encodedZoomLevels){
    int[] out = new int[encodedZoomLevels.length()];
    int index = 0;

    for(char c : encodedZoomLevels.toCharArray())
        out[index++] = c - '?';
    return out;

}
}

Answer 2

您可以使用Google Maps Android API Utility Library.它提出了PolyUtil.decode(String encoded)一种完全符合您需求的方法!