src/tim/prune/function/srtm/TileFinder.java

   1 package tim.prune.function.srtm;
   2
   3 import java.io.InputStream;
   4 import java.net.MalformedURLException;
   5 import java.net.URL;
   6 import java.util.ArrayList;
   7
   8
   9 /**
  10  * Class to get the URLs of the SRTM tiles
  11  * using the srtmtiles.dat file
  12  */
  13 public abstract class TileFinder
  14 {
  15         /** URL prefix for all tiles */
  16         private static final String URL_PREFIX = "https://dds.cr.usgs.gov/srtm/version2_1/SRTM3/";
  17         /** Directory names for each continent */
  18         private static final String[] CONTINENTS = {"", "Eurasia", "North_America", "Australia",
  19                 "Islands", "South_America", "Africa"};
  20
  21
  22         /**
  23          * Get the Urls for the given list of tiles
  24          * @param inTiles list of Tiles to get
  25          * @return array of URLs
  26          */
  27         public static URL[] getUrls(ArrayList<SrtmTile> inTiles)
  28         {
  29                 if (inTiles == null || inTiles.size() < 1) {return null;}
  30                 URL[] urls = new URL[inTiles.size()];
  31                 // Read dat file into array
  32                 byte[] lookup = readDatFile();
  33                 for (int t=0; t<inTiles.size(); t++)
  34                 {
  35                         SrtmTile tile = inTiles.get(t);
  36                         // Get byte from lookup array
  37                         int idx = (tile.getLatitude() + 59)*360 + (tile.getLongitude() + 180);
  38                         try
  39                         {
  40                                 int dir = lookup[idx];
  41                                 if (dir > 0) {
  42                                         try {
  43                                                 urls[t] = new URL(URL_PREFIX + CONTINENTS[dir] + "/" + tile.getTileName());
  44                                         } catch (MalformedURLException e) {} // ignore error, url stays null
  45                                 }
  46                         } catch (ArrayIndexOutOfBoundsException e) {} // ignore error, url stays null
  47                 }
  48                 return urls;
  49         }
  50
  51         /**
  52          * Read the dat file and get the contents
  53          * @return byte array containing file contents
  54          */
  55         private static byte[] readDatFile()
  56         {
  57                 InputStream in = null;
  58                 try
  59                 {
  60                         // Need absolute path to dat file
  61                         in = TileFinder.class.getResourceAsStream("/tim/prune/function/srtm/srtmtiles.dat");
  62                         if (in != null)
  63                         {
  64                                 byte[] buffer = new byte[in.available()];
  65                                 in.read(buffer);
  66                                 in.close();
  67                                 return buffer;
  68                         }
  69                 }
  70                 catch (java.io.IOException e) {
  71                         System.err.println("Exception trying to read srtmtiles.dat : " + e.getMessage());
  72                 }
  73                 finally
  74                 {
  75                         try {
  76                                 in.close();
  77                         }
  78                         catch (Exception e) {} // ignore
  79                 }
  80                 return null;
  81         }
  82 }