使用Google Directions API的Map View绘制路线-解码折线

Question

我正在尝试使用Google路线API在我的地图视图上显示路线，但是我很难从JSON响应中获取数据。我可以获取“级别”和“点”字符串，但无法弄清楚如何将它们解码为地图上的点。

任何帮助将非常感激。

Answer 1

我有一个可以为您解码它们的类，在下面添加该类，然后像这样调用您的代码：

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

您从JSON响应中提取的数据在哪里points和levels。然后，您可以遍历一系列地理点，在它们之间画一条线以显示方向。

希望这可以帮助！肯尼

编辑：似乎Google Directions
API不再将缩放级别字符串作为JSON响应的一部分返回，不过不用担心，我们使用的唯一目的就是检查点数，因此我们可以简单地将它们放入像这样的列表：

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;

}
}