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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 = "http://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;
}
}
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