String getFileName(double lat, double lon) {
        String latStr = getLatString(lat);
        String lonStr = getLonString(lon);
        return toLowerCase(latStr + lonStr);
    }
@Test
    public void testGetFileName() {
        assertEquals("n42e011", instance.getFileName(42.940339, 11.953125));
        assertEquals("n38w078", instance.getFileName(38.548165, -77.167969));
        assertEquals("n14w005", instance.getFileName(14.116047, -4.277344));
        assertEquals("s52w058", instance.getFileName(-51.015725, -57.621094));
        assertEquals("n24e120", instance.getFileName(24.590108, 120.640625));
        assertEquals("s42w063", instance.getFileName(-41.015725, -62.949219));
    }