public static double calAlpha(double theta, double dec) {
if (Math.abs(dec) + theta > 89.9) return 180;
return (double)
Math.toDegrees(
Math.abs(
Math.atan(
Math.sin(Math.toRadians(theta))
/ Math.sqrt(
Math.cos(Math.toRadians(dec - theta))
* Math.cos(Math.toRadians(dec + theta))))));
}
public class NeighborSearch {
public static final int numZones = 180;
public static final int numBlocks = 360;
public static double theta = 1.0 / 60.0;
public static double blockWidth = 360.0 / numBlocks;
public static double zoneHeight = 180.0 / numZones;
private static double blockRanges[][] = new double[numBlocks][2];
private static double zoneRanges[][] = new double[numZones][2];
private static double maxAlphas[] = new double[numZones];
private static double costheta = Math.cos(Math.toRadians(theta));
public static double calAlpha(double theta, double dec) {
if (Math.abs(dec) + theta > 89.9) return 180;
return (double)
Math.toDegrees(
Math.abs(
Math.atan(
Math.sin(Math.toRadians(theta))
/ Math.sqrt(
Math.cos(Math.toRadians(dec - theta))
* Math.cos(Math.toRadians(dec + theta))))));
}
public static void init() {
zoneRanges[0][0] = -90;
zoneRanges[0][1] = -90 + zoneHeight;
for (int i = 1; i < zoneRanges.length; i++) {
zoneRanges[i][0] = zoneRanges[i - 1][1];
zoneRanges[i][1] = zoneRanges[i][0] + zoneHeight;
}
blockRanges[0][0] = 0;
blockRanges[0][1] = blockWidth;
for (int i = 1; i < blockRanges.length; i++) {
blockRanges[i][0] = blockRanges[i - 1][1];
blockRanges[i][1] = blockRanges[i][0] + blockWidth;
}
for (int i = 0; i < maxAlphas.length; i++) {
double maxDec = zoneRanges[i][1];
if (maxDec <= 0) maxDec = zoneRanges[i][0];
maxAlphas[i] = calAlpha(theta, maxDec);
}
}
public static class Map extends MapReduceBase
implements Mapper<LongWritable, Star, BlockIDWritable, PairWritable> {
/* it seems it's very costly to create an object in Java.
* reuse these objects in every map invocation. */
private BlockIDWritable loc = new BlockIDWritable();
private PairWritable p = new PairWritable();
BlockIDWritable loc1 = new BlockIDWritable();
public Map() {
init();
}
public void map(
LongWritable key,
Star value,
OutputCollector<BlockIDWritable, PairWritable> output,
Reporter reporter)
throws IOException {
loc.set(value.ra, value.dec);
int zoneNum = loc.zoneNum;
int raNum = loc.raNum;
p.set(value, null);
/*
* When the block size increases (> theta), only part of a block
* needs to be copied to its neighbor.
*/
output.collect(loc, p);
/*
* only replicate objects in the border of a block. I expect most of
* objects don't need to be copied.
*/
if (value.dec > zoneRanges[zoneNum][0] + theta
&& value.dec < zoneRanges[zoneNum][1] - theta
&& value.ra > blockRanges[raNum][0] + maxAlphas[zoneNum]
&& value.ra < blockRanges[raNum][1] - maxAlphas[zoneNum]) return;
/*
* the code below is to copy the star to some neighbors. We only
* need to copy an object to the bottom, left, left bottom, left top
* neighbors
*/
value.margin = true;
/*
* we should treat the entire zone 0 as a block, so we only needs to
* copy some objects at the corner to their neighbors
*/
if (loc.zoneNum == 0) {
/* copy the object to the right top neighbor */
if (value.ra >= blockRanges[raNum][1] - maxAlphas[zoneNum]
&& value.ra <= blockRanges[raNum][1]
&& value.dec >= zoneRanges[zoneNum][1] - theta
&& value.dec <= zoneRanges[zoneNum][1]) {
// BlockIDWritable loc1 = new BlockIDWritable();
/* raNum of objects in zone 0 is always 0,
* we need to recalculate it. */
// loc1.raNum = BlockIDWritable.ra2Num(value.ra) + 1;
// if (loc1.raNum == numBlocks) {
// loc1.raNum = 0;
// value.ra -= 360;
// }
// loc1.zoneNum = loc.zoneNum + 1;
/// output.collect(loc1, p);
}
return;
} else if (loc.zoneNum == numZones - 1) {
/* copy the object to the bottom neighbor */
if (value.dec >= zoneRanges[zoneNum][0] && value.dec <= zoneRanges[zoneNum][0] + theta) {
/* raNum of objects in zone zoneNum - 1 is always 0,
* we need to recalculate it. */
loc1.raNum = BlockIDWritable.ra2Num(value.ra);
loc1.zoneNum = loc.zoneNum - 1;
output.collect(loc1, p);
/* copy the object to the right bottom neighbor */
while (value.ra >= blockRanges[loc1.raNum][1] - maxAlphas[zoneNum]
&& value.ra <= blockRanges[loc1.raNum][1]) {
loc1.raNum++;
if (loc1.raNum == numBlocks) {
loc1.raNum = 0;
value.ra -= 360;
}
loc1.zoneNum = loc.zoneNum - 1;
output.collect(loc1, p);
}
}
return;
}
boolean wrap = false;
loc1.raNum = loc.raNum;
/* copy the object to the right neighbor */
while (value.ra >= blockRanges[loc1.raNum][1] - maxAlphas[zoneNum]
&& value.ra <= blockRanges[loc1.raNum][1]) {
loc1.raNum++;
loc1.zoneNum = loc.zoneNum;
/*
* when the object is copied to the right neighbor, we need to
* be careful. we need to convert ra and raNum if ra is close to
* 360.
*/
if (loc1.raNum == numBlocks) {
loc1.raNum = 0;
value.ra -= 360;
wrap = true;
}
output.collect(loc1, p);
/* copy the object to the right bottom neighbor */
if (value.dec >= zoneRanges[zoneNum][0] && value.dec <= zoneRanges[zoneNum][0] + theta) {
loc1.zoneNum = loc.zoneNum - 1;
output.collect(loc1, p);
}
/* copy the object to the right top neighbor */
if (value.dec >= zoneRanges[zoneNum][1] - theta && value.dec <= zoneRanges[zoneNum][1]) {
loc1.zoneNum = loc.zoneNum + 1;
output.collect(loc1, p);
}
}
if (wrap) {
value.ra += 360;
}
/* copy the object to the bottom neighbor */
if (value.dec >= zoneRanges[zoneNum][0] && value.dec <= zoneRanges[zoneNum][0] + theta) {
loc1.raNum = loc.raNum;
loc1.zoneNum = loc.zoneNum - 1;
if (loc1.zoneNum == 0) loc1.raNum = 0;
output.collect(loc1, p);
}
}
}
public static class Reduce extends MapReduceBase
implements Reducer<BlockIDWritable, PairWritable, BlockIDWritable, PairWritable> {
PairWritable p = new PairWritable();
public Reduce() {
init();
}
void search(
Vector<Star> v1,
Vector<Star> v2,
BlockIDWritable key,
OutputCollector<BlockIDWritable, PairWritable> output)
throws IOException {
for (int i = 0; i < v1.size(); i++) {
for (int j = 0; j < v2.size(); j++) {
Star star1 = v1.get(i);
Star star2 = v2.get(j);
// what is this margin about
if (star1.margin && star2.margin) continue;
double dist = star1.x * star2.x + star1.y * star2.y + star1.z * star2.z;
if (dist > costheta) {
p.set(star1, star2, dist);
output.collect(key, p);
p.set(star2, star1, dist);
output.collect(key, p);
// num += 2;
}
}
} // end for i,j
}
public void reduce(
BlockIDWritable key,
Iterator<PairWritable> values,
OutputCollector<BlockIDWritable, PairWritable> output,
Reporter reporter)
throws IOException {
// Vector<Star> starV = new Vector<Star>();
int buketsizeX = 0;
int buketsizeY = 0;
double bwidth = maxAlphas[key.zoneNum]; // ra ,x
double bheight = theta; // dec ,y
/* add 10 more in each dimension to make sure there is no overflow. */
Vector<Star>[][] arrstarV =
new Vector[((int) (zoneHeight / bheight)) + 10]
[((int) (blockWidth / bwidth)) + 10]; // create bucket vector[Y][X]
int num = 0;
while (values.hasNext()) {
num++;
Star s = values.next().get(0);
// participant
double posx = (s.ra - blockRanges[key.raNum][0]) / bwidth;
int x = (int) posx + 1; // shit by 1 in case star comes from other block
double posy = (s.dec - zoneRanges[key.zoneNum][0]) / bheight;
int y = (int) posy + 1;
// set bucket size as max
if (buketsizeX < x) buketsizeX = x;
if (buketsizeY < y) buketsizeY = y;
// create according bucket
if (arrstarV[y][x] == null)
// TODO avaoid creating vectors here.
arrstarV[y][x] = new Vector<Star>();
// put star into bucket
arrstarV[y][x].add(s);
}
// start reducer
int i, j, row, col;
// for each bucket
for (row = 0; row <= buketsizeY; row++) {
for (col = 0; col <= buketsizeX; col++) {
// starV.clear();
// construct a new vector to do compare
// TODO we need to avoid searching objects in the border.
if (arrstarV[row][col] != null) {
// old method to generate output
for (i = 0; i < arrstarV[row][col].size(); i++) {
for (j = i + 1; j < arrstarV[row][col].size(); j++) {
Star star1 = arrstarV[row][col].get(i);
Star star2 = arrstarV[row][col].get(j);
// what is this margin about
if (star1.margin && star2.margin) continue;
double dist = star1.x * star2.x + star1.y * star2.y + star1.z * star2.z;
if (dist > costheta) {
p.set(star1, star2, dist);
output.collect(key, p);
p.set(star2, star1, dist);
output.collect(key, p);
// num += 2;
}
}
} // end for i,j
} // end if
else {
continue;
}
// 4 more neighbors
// right upper arrstarV[row-1][col+1] vs arrstarV[row][col]
if (row != 0 && arrstarV[row - 1][col + 1] != null) {
search(arrstarV[row][col], arrstarV[row - 1][col + 1], key, output);
}
// right arrstarV[row][col+1] vs arrstarV[row][col]
if (arrstarV[row][col + 1] != null) {
search(arrstarV[row][col], arrstarV[row][col + 1], key, output);
}
// right lower
if (arrstarV[row + 1][col + 1] != null) {
search(arrstarV[row][col], arrstarV[row + 1][col + 1], key, output);
}
// lower
if (arrstarV[row + 1][col] != null) {
search(arrstarV[row][col], arrstarV[row + 1][col], key, output);
} // end if
} // end colum
} // end row
}
}
public static void main(String[] args) throws Exception {
JobConf conf = new JobConf(NeighborSearch.class);
conf.setJobName("star searching");
conf.setOutputKeyClass(BlockIDWritable.class);
conf.setOutputValueClass(PairWritable.class);
conf.setMapperClass(Map.class);
// conf.setCombinerClass(Reduce.class);
conf.setReducerClass(Reduce.class);
// conf.setPartitionerClass(BlockPartitioner.class);
// conf.setFloat("mapred.reduce.slowstart.completed.maps", (float) 1.0);
conf.setInputFormat(StarInputFormat.class);
conf.setOutputFormat(StarOutputFormat.class);
FileInputFormat.setInputPaths(conf, new Path(args[0]));
FileOutputFormat.setOutputPath(conf, new Path(args[1]));
JobClient.runJob(conf);
}
}