String getDownloadURL(double lat, double lon) {
        String latStr = getLatString(lat);
        String lonStr = getLonString(lon);

        return latStr + "/" + latStr + lonStr + ".hgt.gz";
    }
@Test
    public void testGetDownloadUrl() {
        assertEquals("N42/N42E011.hgt.gz", instance.getDownloadURL(42.940339, 11.953125));
        assertEquals("N38/N38W078.hgt.gz", instance.getDownloadURL(38.548165, -77.167969));
        assertEquals("N14/N14W005.hgt.gz", instance.getDownloadURL(14.116047, -4.277344));
        assertEquals("S52/S52W058.hgt.gz", instance.getDownloadURL(-51.015725, -57.621094));
        assertEquals("N24/N24E120.hgt.gz", instance.getDownloadURL(24.590108, 120.640625));
        assertEquals("S42/S42W063.hgt.gz", instance.getDownloadURL(-41.015725, -62.949219));
    }