我试图使用Google directions API来显示我的地图视图中的路线,但是我无法从
JSON响应中获取数据.我可以得到“水平”和“点”字符串,但无法解决如何将它们解码到地图上的点.
任何帮助将不胜感激.
解决方法
我有一个类可以为你解码,添加下面的类,然后调用你的代码,如下所示：
int[] decodedZoomLevels = PolylineDecoder.decodeZoomLevels(levels); GeoPoint[] gPts = PolylineDecoder.decodePoints(points,decodedZoomLevels.length);
点数和级别是您从JSON响应中提取的数据.然后,您可以浏览一系列地理点,在它们之间绘制一条线,以显示您的路线.
希望这可以帮助！肯尼
编辑：似乎google directions API不再返回缩放级别字符串作为JSON响应的一部分,不用担心,但是我们所使用的都是检查点数,所以我们可以简单地将它们放入列表如下：
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：旧版
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;
}
}
