The original implementation can be found here: http://www.khelekore.org/prtree/index.shtml
This is a mirror that has been Maven-ized.
PRTree is a Priority R-Tree, a spatial index.
For some background read this: http://www.cs.umd.edu/class/spring2005/cmsc828s/slides/prtree.pdf
PRTree is written to be fast and use as little memory aspossible.
The source for org.khelekore.prtree.junit.TestRTree has a few examples of setting up and querying a PRTree.
Basic usage goes something like this:
PRTree<Rectangle2D> tree =
new PRTree<Rectangle2D> (new Rectangle2DConverter (), 10);
Rectangle2D rx = new Rectangle2D.Double (0, 0, 1, 1);
tree.load (Collections.singletonList (rx));
for (Rectangle2D r : tree.find (0, 0, 1, 1)) {
System.out.println ("found a rectangle: " + r);
}