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

   1 package tim.prune.function.srtm;
   2
   3 import java.io.File;
   4 import java.io.FileInputStream;
   5 import java.io.FileOutputStream;
   6 import java.io.IOException;
   7 import java.util.zip.ZipEntry;
   8 import java.util.zip.ZipInputStream;
   9
  10 public abstract class SrtmSource {
  11         public abstract String getName();
  12         public abstract boolean isReadyToUse();
  13         public abstract boolean downloadTile(SrtmTile inTile)
  14                 throws SrtmSourceException;
  15         public abstract int getRowSize(SrtmTile inTile);
  16         protected abstract String getSourceExtension();
  17
  18         protected int[] slurpTileHeigths(ZipInputStream inStream, int tileSize)
  19                 throws IOException
  20         {
  21                 int[] heights = new int[tileSize];
  22                 int dataSize = 2 * tileSize;
  23                 byte[] buffer = new byte[dataSize];
  24                 // Read entire file contents into one byte array
  25                 int alreadyRead = 0;
  26                 while (alreadyRead < dataSize)
  27                 {
  28                         alreadyRead += inStream.read(buffer, alreadyRead, dataSize - alreadyRead);
  29                 }
  30                 for (int i = 0; i < tileSize; i++)
  31                 {
  32                         // Bytes are signed. Cast high-order to int with sign
  33                         // extension, and clamp low-order to its unsigned range
  34                         heights[i] = buffer[2 * i] * 256 + (0xff & buffer[2 * i + 1]);
  35                 }
  36                 // Close stream
  37                 inStream.close();
  38                 return heights;
  39         }
  40
  41         public int[] getTileHeights(SrtmTile inTile)
  42                 throws SrtmSourceException
  43         {
  44                 File cacheFileName = getCacheFileName(inTile);
  45                 if (cacheFileName == null)
  46                 {
  47                         throw new SrtmSourceException("Tile "+inTile.getTileName()+" not in cache");
  48                 }
  49                 try
  50                 {
  51                         ZipInputStream inStream = new ZipInputStream(new FileInputStream(cacheFileName));
  52                         ZipEntry entry = inStream.getNextEntry();
  53                         int rowSize = getRowSize(inTile);
  54                         int tileSize = rowSize * rowSize;
  55                         if (entry.getSize() != 2 * tileSize)
  56                         {
  57                                 throw new SrtmSourceException("Tile file "+cacheFileName+" does not have the expected size");
  58                         }
  59                         return slurpTileHeigths(inStream, tileSize);
  60                 }
  61                 catch (IOException e)
  62                 {
  63                         throw new SrtmSourceException("Failure opening "+cacheFileName+" for reading:"+e.getMessage());
  64                 }
  65
  66         }
  67
  68         protected File getCacheDir()
  69         {
  70                 return SrtmDiskCache.getCacheDir(getName());
  71         }
  72
  73         protected File getCacheFileName(SrtmTile inTile)
  74         {
  75                 String fileName = inTile.getTileName() + getSourceExtension();
  76                 return new File(getCacheDir(), fileName);
  77         }
  78
  79         public boolean isCached(SrtmTile inTile)
  80         {
  81                 File cachedFileName = getCacheFileName(inTile);
  82                 return cachedFileName != null &&
  83                         getCacheFileName(inTile).exists();
  84         }
  85 }