question: public static String encode ( ArrayList < GeoPoint > polyline , int precision ) { StringBuilder encodedPoints = new StringBuilder ( ) ; int prev_lat = 0 , prev_lng = 0 ; for ( GeoPoint trackpoint : polyline ) { int lat = trackpoint . getLatitudeE6 ( ) / precision ; int lng = trackpoint . getLongitudeE6 ( ) / precision ; encodedPoints . append ( encodeSignedNumber ( lat - prev_lat ) ) ; encodedPoints . append ( encodeSignedNumber ( lng - prev_lng ) ) ; prev_lat = lat ; prev_lng = lng ; } return encodedPoints . toString ( ) ; }
target:  Encode a polyline with Google polyline encoding method