Pass SQLite marks to Google Maps

I have a SQLite database where the marks are stored but I am not able to load them on the map. Thank you very much for your time.

Main activity

public class MapsActivity extends FragmentActivity implements OnMapReadyCallback {

Button btn;
Context context = this;
private GoogleMap mMap;
SQLiteDatabase db=null;
Cursor cursor=null;
LatLng latLng;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate ( savedInstanceState );
    setContentView ( R.layout.activity_maps );
    btn = (Button) findViewById ( R.id.btnBuscar );
    // Obtain the SupportMapFragment and get notified when the map is ready to be used.
    SupportMapFragment mapFragment = (SupportMapFragment) getSupportFragmentManager ()
            .findFragmentById ( R.id.map );
    mapFragment.getMapAsync ( this );

} // FIN METODO ONCREATE

@Override
public void onMapReady(GoogleMap googleMap) {
    mMap = googleMap;

    // Add a marker in Sydney and move the camera
    CameraUpdate camUpd1 =
            CameraUpdateFactory
                    .newLatLngZoom(new LatLng(40.41, -3.69), 5);

    mMap.moveCamera(camUpd1);

    mMap.setOnMapLongClickListener ( new GoogleMap.OnMapLongClickListener () {

        @Override
        public void onMapLongClick(final LatLng latLng) {

        // ALERTDIALOG PARA ELEGIR ICONO
            final AlertDialog.Builder builder= new AlertDialog.Builder ( MapsActivity.this );
            LayoutInflater inflater =(LayoutInflater)getApplicationContext ().getSystemService ( Context.LAYOUT_INFLATER_SERVICE );
            View row = inflater.inflate ( R.layout.row_item,null );
            ListView listView = (ListView)row.findViewById ( R.id.lvIconosMapa );
            listView.setAdapter ( new CustomAdapter ( getApplicationContext () ) );
            builder.setView ( row );

            // TITULO DEL ALERTDIALOG CUSTOMIZADO
            final TextView title = new TextView(MapsActivity.this);
            title.setText("Elija una opción");
            title.setBackgroundColor(Color.BLUE);
            title.setPadding(10, 10, 10, 10);
            title.setGravity(Gravity.CENTER);
            title.setTextColor(Color.BLACK);
            title.setTextSize(20);
            builder.setCustomTitle(title);

            builder.setNegativeButton ( "Cancelar", null );
            final AlertDialog dialog = builder.create ();
            dialog.show ();
            // FIN ALERTDIALOG

        listView.setOnItemClickListener ( new AdapterView.OnItemClickListener () {
            @Override
            public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
                if (position==0){
                         mMap.addMarker ( new MarkerOptions ()
                            .title ( "Titulo" )
                            .icon ( BitmapDescriptorFactory.fromResource (R.drawable.avion ) )
                            .anchor ( 0.0f,1.0f )
                            .snippet ( "Descripcion" )
                            .position ( latLng ));
                    Double latitud = latLng.latitude;
                    Double longitud = latLng.longitude;
                    Intent intent = new Intent ( getApplicationContext (), MainActivity.class );
                    intent.putExtra ( "LATITUD", latitud );
                    intent.putExtra ( "LONGITUD", longitud );
                    intent.putExtra ( "ICONO", R.drawable.avion );
                    intent.putExtra ( "FECHA", "HOY" );
                    startActivity ( intent);
                }
                else if (position==1){
                    mMap.addMarker ( new MarkerOptions ()
                            .icon ( BitmapDescriptorFactory.fromResource (R.drawable.coche ) )
                            .anchor ( 0.0f,1.0f )
                            .position ( latLng ));
                             dialog.cancel ();
                }

            }

        } );

        }


    } );

    mMap.setOnMarkerClickListener ( new GoogleMap.OnMarkerClickListener () {
        @Override
        public boolean onMarkerClick(Marker marker) {
            Toast.makeText ( getApplicationContext (), marker.getId (), Toast.LENGTH_SHORT ).show ();
            return true;
        }
    } );
}

Database

public class BBDD_Helper extends SQLiteOpenHelper {


public static final int DATABASE_VERSION = 1;
public static final String DATABASE_NAME = "marcas.db";
private final Context myContext;
private BBDD_Helper dbHelper;
private SQLiteDatabase db;
/**
 * Definimos constantes con el nombre de las columnas de la tabla
 */
public static final String C_COLUMNA_ID   = "_id";
public static final String C_COLUMNA_NOMBRE = "nombre";
public static final String C_COLUMNA_LAT = "lat";
public static final String C_COLUMNA_LON = "lon";
public static final String C_COLUMNA_DESCRIPCION = "descripcion";
public static final String C_COLUMNA_ICONO = "icono";
public static final String C_COLUMNA_FECHA = "fecha";

String slqCreate = "CREATE TABLE tablamarcas (_id INTEGER PRIMARY KEY AUTOINCREMENT," + " nombre TEXT, lat DOUBLE, lon DOUBLE, descripcion TEXT, icono INTEGER, fecha TEXT)";

String sqlUpdate = "ALTER TABLE tablamarcas ADD COLUMN fecha TEXT;";

private String[] columnas = new String[]{ C_COLUMNA_ID, C_COLUMNA_NOMBRE, C_COLUMNA_LAT, C_COLUMNA_LON, C_COLUMNA_DESCRIPCION, C_COLUMNA_ICONO, C_COLUMNA_FECHA} ;

public BBDD_Helper(Context context, String nombre, SQLiteDatabase.CursorFactory factory, int version) {
    super(context, DATABASE_NAME, null, DATABASE_VERSION);
    this.myContext = context;
}

@Override
public void onCreate(SQLiteDatabase db) {
    if (db.isReadOnly ()){
        db = getWritableDatabase ();
    }
    db.execSQL(slqCreate);

}

@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {

    if (newVersion > oldVersion){
        db.execSQL ( sqlUpdate );
    }
}


public BBDD_Helper abrir() throws SQLException
{
    dbHelper = new BBDD_Helper (myContext, DATABASE_NAME, null, DATABASE_VERSION);
    db = dbHelper.getWritableDatabase();
    return this;
}

public void cerrar()
{
    dbHelper.close();
}

/**
 * Devuelve cursor con todos las columnas de la tabla
 */
public Cursor getCursor() throws SQLException
{
    Cursor c = db.query( true, BBDD.BBDD_Estructura.TABLE_NAME, columnas, null, null, null, null, null, null);

    return c;
}