Reading ASTER DEM Data

[Ahmad]

Hi,

How can I read ASTER DEM data set.
http://en.wikipedia.org/wiki/Advanced_Spaceborne_Thermal_Emission_and_Reflection_Radiometer

I have folder that contains tiles of ASTER in tif format, and I want
to write a function that take lon/lat as arguments and return a number
as an elevation.

I wrote a class in Java to do that, but I think I have something
wrong. The readings seems not to be correct!

import java.util.concurrent.ConcurrentHashMap;

import javax.media.jai.JAI;
import javax.media.jai.PlanarImage;
import javax.media.jai.iterator.RandomIter;
import javax.media.jai.iterator.RandomIterFactory;

public class AsterDemReader implements DemProvider {

// base path for the tiles
private String basePath;

// tiles RAM cache
private ConcurrentHashMap<String, RandomIter> cache = new
ConcurrentHashMap<String, RandomIter>();

public AsterDemReader(String basePath) {
this.basePath = basePath;
}

private RandomIter getTile(String tileName) {
RandomIter iter = cache.get(tileName);
if (iter == null) {
PlanarImage image = JAI.create("fileload", String.format(
"%s/ASTGTM_%s_dem.tif", basePath, tileName));
iter = RandomIterFactory.create(image, null);
cache.put(tileName, iter);
}
return iter;
}

// lat and lon in decimal degrees
/*
* (non-Javadoc)
*
*
*/
public double getElevation(double lat, double lon) throws
Exception {

lat -= .0001389;
lon -= .0001389;

// file name
int latDegree = (int) Math.abs(lat);
int lonDegree = (int) Math.abs(lon);

char northSouth = (lat < 0) ? 'E' : 'N';
char eastWest = (lon < 0) ? 'W' : 'E';

String tileName = String.format("%c%2d%c%3d", northSouth,
latDegree,
eastWest, lonDegree).replace(" ", "0");
// the frection only
lat -= (int) lat;
lon -= (int) lon;

lat = Math.abs(lat);
lon = Math.abs(lon);

// calculate x and y of the image
int y = 3600 - (int) (3600 * lat);
int x = (int) (3600 * lon);
// System.out.println(String.format("x=%d y=%d", x, y));

// get the image from cache

RandomIter iter = getTile(tileName);
double av = iter.getSampleDouble(x, y, 0);

return av;
}

public static void main(String args[]) throws Exception {
DemProvider aster = new AsterDemReader("D:/OldHP");
double elev = aster.getElevation(33.5, 42.5);

System.out.println(elev);
}
}

Could anyone please point me where I'm getting wrong? where can I find
more info about reading ASTER DEM?

Best Regards,

[jeanh]

Ahmad,

you are not providing enough information about your data and your GIS.

From your code, I would focus on how you compute the X;Y coordinates.
You are not considering any projection nor any resolution and you assume
that the north is straight up. I suggest you to search the available
libraries for doing such conversion.

Jean