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Decoding polyline with new Google Maps API

由 牧云@^-^@ 提交于 2019-11-28 04:24:12

I changed the decodePoly that I was using for this one I found after a long search in Google, and now the route is drawn properly.

http://wptrafficanalyzer.in/blog/route-between-two-locations-with-waypoints-in-google-map-android-api-v2/

Changing 

LatLng p = new LatLng((int) (((double) lat /1E5)* 1E6), (int) (((double) lng/1E5   * 1E6)));

for 

LatLng p = new LatLng((((double) lat / 1E5)),(((double) lng / 1E5)));

And now works.

CounterFlame

For those who need this now, there's an open-source library with a lot of useful stuff regarding the Google Maps Android API, including decoding and encoding of polylines.

Check it out at Android Maps Utils and Android Maps Util Github. For decoding and encoding use:

PolyUtil.decode(String encodedPath);
PolyUtil.encode(List<LatLng> path);
L. Zampetti

Same in Javascript

    function decodePolyline(encoded) {
        if (!encoded) {
            return [];
        }
        var poly = [];
        var index = 0, len = encoded.length;
        var lat = 0, lng = 0;

        while (index < len) {
            var b, shift = 0, result = 0;

            do {
                b = encoded.charCodeAt(index++) - 63;
                result = result | ((b & 0x1f) << shift);
                shift += 5;
            } while (b >= 0x20);

            var dlat = (result & 1) != 0 ? ~(result >> 1) : (result >> 1);
            lat += dlat;

            shift = 0;
            result = 0;

            do {
                b = encoded.charCodeAt(index++) - 63;
                result = result | ((b & 0x1f) << shift);
                shift += 5;
            } while (b >= 0x20);

            var dlng = (result & 1) != 0 ? ~(result >> 1) : (result >> 1);
            lng += dlng;

            var p = {
                latitude: lat / 1e5,
                longitude: lng / 1e5,
            };
            poly.push(p);
        }
        return poly;
    }

This method is useful for decoding polyline

 private List<LatLng> decodePoly(String encoded) {
    List<LatLng> poly = new ArrayList<>();
    int index = 0, len = encoded.length();
    int lat = 0, lng = 0;

    while (index < len) {
        int b, shift = 0, result = 0;
        do {
            b = encoded.charAt(index++) - 63;
            result |= (b & 0x1f) << shift;
            shift += 5;
        } while (b >= 0x20);
        int dlat = ((result & 1) != 0 ? ~(result >> 1) : (result >> 1));
        lat += dlat;

        shift = 0;
        result = 0;
        do {
            b = encoded.charAt(index++) - 63;
            result |= (b & 0x1f) << shift;
            shift += 5;
        } while (b >= 0x20);
        int dlng = ((result & 1) != 0 ? ~(result >> 1) : (result >> 1));
        lng += dlng;

        LatLng p = new LatLng((((double) lat / 1E5)),
                (((double) lng / 1E5)));
        poly.add(p);
    }

    return poly;
}

This is how i'm getting polyline

JSONObject poly = route.getJSONObject("overview_polyline");
String polyline = poly.getString("points");
polyLineList = decodePoly(polyline);
Alexey Ivakhin

Same in Pascal (Delphi):

function DecodeLine(inputstring: String): String;
var
  lat, lon, lat_f, lon_f: Double;
  index: Integer;
  len: Integer;
  b: Integer;
  shift: Integer;
  decodeResult: Integer;
  encoded: String;
  dlat: Integer;
  dlng: Integer;
begin
  Result := '';

  encoded := inputstring;
  len := Length(encoded);
  index := 1;
  lat := 0;
  lon := 0;

  while (index <= len) do begin
    b := $20;
    shift := 0;
    decodeResult := 0;

    while (b >= $20) do begin
      b := ord(encoded[index]);
      b := b - 63;
      inc(index);
      decodeResult := decodeResult or (b and $1f) Shl shift;
      shift := shift + 5;
    end;

    if (decodeResult and 1) <> 0 then
      dlat := not (decodeResult shr 1)
    else
      dlat := decodeResult shr 1;
    lat := lat+dlat;

    shift := 0;
    decodeResult := 0;
    b := $20;
    while (b >= $20) do begin
      b := ord(encoded[index]);
      b := b-63;
      inc(index);
      decodeResult := decodeResult or (b and $1f) Shl shift;
      shift := shift + 5;
    end;

    if (decodeResult and 1) <> 0 then
      dlng := not (decodeResult shr 1)
    else
      dlng := decodeResult shr 1;
    lon := lon + dlng;

    { The coordinates of the point are used for our purposes }
    lon_f := lon/100000.0;
    lat_f := lat/100000.0;

    if Result <> '' then
      Result := Result + ', ';
    Result := Result + '(' + FloatToStr(lon_f) + ' - ' + FloatToStr(lat_f) + ')';
  end; //while
end;


procedure TForm1.Button1Click(Sender: TObject);
var
  str: String;
begin
  // Do stuff
  str := DecodeLine('ibgqGq}ycIMvM');
  ShowMessage(str);
end;

Here is the implementation in iOS, for anybody who is curious, which is entirely based upon @Fustigador's answer, but converted to iOS. Note that I have not formatted the code accordingly. I only added some variables for the sake of returning the promised object.

- (GMSPath *)decodedPolylinePathFromEncodedPolylineString:(NSString *)encodedPolylineString {


    NSString *decodedPolylineString = @"";
    GMSMutablePath *decodedPolylinePath = [GMSMutablePath new];
    CLLocationCoordinate2D decodedCoordinate;
    CLLocationDegrees latitude, longitude;

    int index = 0;
    NSUInteger len = encodedPolylineString.length;

    int lat = 0, lng = 0;

    while (index < len) {
        int b, shift = 0, result = 0;
        do {

            b = [encodedPolylineString characterAtIndex:index++] - 63;
            result |= (b & 0x1f) << shift;
            shift += 5;
        } while (b >= 0x20);
        int dlat = ((result & 1) != 0 ? ~(result >> 1) : (result >> 1));
        lat += dlat;

        shift = 0;
        result = 0;
        do {
            b = [encodedPolylineString characterAtIndex:index++] - 63;
            result |= (b & 0x1f) << shift;
            shift += 5;
        } while (b >= 0x20);
        int dlng = ((result & 1) != 0 ? ~(result >> 1) : (result >> 1));
        lng += dlng;

        latitude =  (((double) lat / 1E5));
        longitude = (((double) lng / 1E5));

        decodedCoordinate = CLLocationCoordinate2DMake(latitude, longitude);

        decodedPolylineString = [NSString stringWithFormat:@"%f%f", latitude, longitude];
        ;
        NSLog(@"%@",decodedPolylineString);

        [decodedPolylinePath addCoordinate:decodedCoordinate];
    }


    return decodedPolylinePath;
}
标签
android
google-maps
polyline
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