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                 if (lookup == null)
  34                 {
  35                         System.err.println("Build error: resource srtmtiles.dat missing!");
  36                         return null;
  37                 }
  38                 for (int t=0; t<inTiles.size(); t++)
  39                 {
  40                         SrtmTile tile = inTiles.get(t);
  41                         // Get byte from lookup array
  42                         int idx = (tile.getLatitude() + 59)*360 + (tile.getLongitude() + 180);
  43                         try
  44                         {
  45                                 int dir = lookup[idx];
  46                                 if (dir > 0) {
  47                                         try {
  48                                                 urls[t] = new URL(URL_PREFIX + CONTINENTS[dir] + "/" + tile.getTileName());
  49                                         } catch (MalformedURLException e) {} // ignore error, url stays null
  50                                 }
  51                         } catch (ArrayIndexOutOfBoundsException e) {} // ignore error, url stays null
  52                 }
  53                 return urls;
  54         }
  55
  56         /**
  57          * Read the dat file and get the contents
  58          * @return byte array containing file contents
  59          */
  60         private static byte[] readDatFile()
  61         {
  62                 InputStream in = null;
  63                 try
  64                 {
  65                         // Need absolute path to dat file
  66                         in = TileFinder.class.getResourceAsStream("/tim/prune/function/srtm/srtmtiles.dat");
  67                         if (in != null)
  68                         {
  69                                 byte[] buffer = new byte[in.available()];
  70                                 in.read(buffer);
  71                                 in.close();
  72                                 return buffer;
  73                         }
  74                 }
  75                 catch (java.io.IOException e) {
  76                         System.err.println("Exception trying to read srtmtiles.dat : " + e.getMessage());
  77                 }
  78                 finally
  79                 {
  80                         try {
  81                                 in.close();
  82                         }
  83                         catch (Exception e) {} // ignore
  84                 }
  85                 return null;
  86         }
  87 }