+package tim.prune.function.srtm;
+
+import java.io.InputStream;
+import java.net.MalformedURLException;
+import java.net.URL;
+import java.util.ArrayList;
+
+
+/**
+ * Class to get the URLs of the SRTM tiles
+ * using the srtmtiles.dat file
+ */
+public abstract class TileFinder
+{
+ /** URL prefix for all tiles */
+ private static final String URL_PREFIX = "https://dds.cr.usgs.gov/srtm/version2_1/SRTM3/";
+ /** Directory names for each continent */
+ private static final String[] CONTINENTS = {"", "Eurasia", "North_America", "Australia",
+ "Islands", "South_America", "Africa"};
+
+
+ /**
+ * Get the Urls for the given list of tiles
+ * @param inTiles list of Tiles to get
+ * @return array of URLs
+ */
+ public static URL[] getUrls(ArrayList<SrtmTile> inTiles)
+ {
+ if (inTiles == null || inTiles.size() < 1) {return null;}
+ URL[] urls = new URL[inTiles.size()];
+ // Read dat file into array
+ byte[] lookup = readDatFile();
+ for (int t=0; t<inTiles.size(); t++)
+ {
+ SrtmTile tile = inTiles.get(t);
+ // Get byte from lookup array
+ int idx = (tile.getLatitude() + 59)*360 + (tile.getLongitude() + 180);
+ try
+ {
+ int dir = lookup[idx];
+ if (dir > 0) {
+ try {
+ urls[t] = new URL(URL_PREFIX + CONTINENTS[dir] + "/" + tile.getTileName());
+ } catch (MalformedURLException e) {} // ignore error, url stays null
+ }
+ } catch (ArrayIndexOutOfBoundsException e) {} // ignore error, url stays null
+ }
+ return urls;
+ }
+
+ /**
+ * Read the dat file and get the contents
+ * @return byte array containing file contents
+ */
+ private static byte[] readDatFile()
+ {
+ InputStream in = null;
+ try
+ {
+ // Need absolute path to dat file
+ in = TileFinder.class.getResourceAsStream("/tim/prune/function/srtm/srtmtiles.dat");
+ if (in != null)
+ {
+ byte[] buffer = new byte[in.available()];
+ in.read(buffer);
+ in.close();
+ return buffer;
+ }
+ }
+ catch (java.io.IOException e) {
+ System.err.println("Exception trying to read srtmtiles.dat : " + e.getMessage());
+ }
+ finally
+ {
+ try {
+ in.close();
+ }
+ catch (Exception e) {} // ignore
+ }
+ return null;
+ }
+}