Add polyline encoding and decoding

[RaimundWege]

As a developer I want to encode and decode polylines.

The following code can be used for decoding:

List<LatLng> decodePolyline(String encoded) {
  List<LatLng> points = new List<LatLng>();
  int index = 0, len = encoded.length;
  int lat = 0, lng = 0;
  while (index < len) {
    int b, shift = 0, result = 0;
    do {
      b = encoded.codeUnitAt(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.codeUnitAt(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(lat / 1E5, lng / 1E5);
    points.add(p);
  }
  return points;
}

[johnpryan]

PolylineLayer takes a List<LatLng> already. Why does this function need to be included in the flutter_map project?

[RaimundWege]

Eventually I miss something but many REST APIs return a polyline as an encoded String (like `~oia@ source: https://developers.google.com/maps/documentation/utilities/polylinealgorithm) and as a developer I want to write something like

Polyline polyline = new Polyline(encodedPoints: "`~oia@", color: Colors.blue);

or

print(polyline.encode()); // -> `~oia@

[johnpryan]

Is there a reason you can't build this as a separate package?

[RaimundWege]

No. So I (or someone else) should publish this as a separate package? If so we can close this issue.

[johnpryan]

Yes I think that makes sense in this case, thanks!

[bijoya-banik]

Thank u, it works nicely

[aloenobilis]

Hi,
@RaimundWege @johnpryan recently published polyline.dart - https://github.com/sashvoncurtis/polyline.dart

Using flutter map I then use polyline.dart and decode the encoded string into a list of decoded coordinates.

[aloenobilis]

Hi,
@RaimundWege @johnpryan recently published polyline.dart - https://github.com/sashvoncurtis/polyline.dart

Using flutter map I then use polyline.dart and decode the encoded string into a list of decoded coordinates.

[johnpryan]

@sashvoncurtis very cool!