地图视图使用 google Directions API 绘制方向 - 解码折线 [英] Map View draw directions using google Directions API - decoding polylines

问题描述

我正在尝试使用 Google 路线 API 在我的地图视图上显示路线，但我无法从 JSON 响应中获取数据.我可以获得levels"和points"字符串，但不知道如何将它们解码为地图上的点.

I'm trying to use the Google directions API to show directions on my mapview but I am having difficulties getting the data from the JSON response. I can get the "levels" and "points" strings but can't work out how to decode them to points on the map.

任何帮助将不胜感激.

推荐答案

我有一个类可以为你解码它们，添加下面的类然后像这样调用你的代码:

I have a class which can decode them for you, add the class below then call in your code like this:

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

其中 points 和 levels 是您从 JSON 响应中提取的数据.然后，您可以遍历地理点数组，在它们之间画一条线以显示您的方向.

where points and levels are the data you've extracted from the JSON response. You can then go through the array of geopoints drawing a line between them to display your directions.

希望这有帮助！肯尼

似乎谷歌路线 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，我们使用它只是为了检查点数，所以我们可以简单地将这些放入一个列表中，例如:

It would seem that the google directions API no longer returns the zoom levels string as part of the JSON response, not to worry though, all we were using this for was to check the number of points, so we can simply put these into a list like:

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;
}

<小时>

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;

}
}

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