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
   7
   8 /**
   9  * Class to get the URLs of the SRTM tiles
  10  * using the srtmtiles.dat file
  11  */
  12 public class TileFinder
  13 {
  14         /** tile data loaded from file */
  15         private byte[] _tileData = null;
  16
  17         /** URL prefix for all tiles */
  18         private static final String URL_PREFIX = "https://dds.cr.usgs.gov/srtm/version2_1/SRTM3/";
  19         /** Directory names for each continent */
  20         private static final String[] CONTINENTS = {"", "Eurasia", "North_America", "Australia",
  21                 "Islands", "South_America", "Africa"};
  22
  23
  24         /**
  25          * Get the Urls for the given list of tiles
  26          * @param inTiles list of Tiles to get
  27          * @return array of URLs
  28          */
  29         public URL getUrl(SrtmTile inTile)
  30         {
  31                 if (inTile == null) {return null;}
  32                 if (_tileData == null)
  33                 {
  34                         _tileData = readDatFile();
  35                         if (_tileData == null)
  36                         {
  37                                 System.err.println("Build error: resource srtmtiles.dat missing!");
  38                                 return null;
  39                         }
  40                 }
  41
  42                 URL url = null;
  43                 // Get byte from lookup array
  44                 int idx = (inTile.getLatitude() + 59)*360 + (inTile.getLongitude() + 180);
  45                 try
  46                 {
  47                         int dir = _tileData[idx];
  48                         if (dir > 0) {
  49                                 try {
  50                                         url = new URL(URL_PREFIX + CONTINENTS[dir] + "/" + inTile.getTileName());
  51                                 } catch (MalformedURLException e) {} // ignore error, url stays null
  52                         }
  53                 } catch (ArrayIndexOutOfBoundsException e) {} // ignore error, url stays null
  54
  55                 return url;
  56         }
  57
  58         /**
  59          * Read the dat file and get the contents
  60          * @return byte array containing file contents
  61          */
  62         private static byte[] readDatFile()
  63         {
  64                 InputStream in = null;
  65                 try
  66                 {
  67                         // Need absolute path to dat file
  68                         in = TileFinder.class.getResourceAsStream("/tim/prune/function/srtm/srtmtiles.dat");
  69                         if (in != null)
  70                         {
  71                                 byte[] buffer = new byte[in.available()];
  72                                 in.read(buffer);
  73                                 in.close();
  74                                 return buffer;
  75                         }
  76                 }
  77                 catch (java.io.IOException e) {
  78                         System.err.println("Exception trying to read srtmtiles.dat : " + e.getMessage());
  79                 }
  80                 finally
  81                 {
  82                         try {
  83                                 in.close();
  84                         }
  85                         catch (Exception e) {} // ignore
  86                 }
  87                 return null;
  88         }
  89 }