A Java package for doing spherical trigonometry without all the messy (and cpu intensive) trigonometry. The spheres package includes classes for points, spherical polygons, latitude/longitude bounding boxes, orbits, and scenes. Spheres documentation includes a variety of algorithm descriptions for performing areal comparisons on the sphere.
The spheres package itself performs areal comparisons on the sphere for spherical polygons, lat/lon bounding boxes, orbits, and scenes. The javadoc documentation is on-line to give you an idea of what it does, or should do. The source code and the class files are also available in separate jar files (right click and "save as"). Or, if you're really keen, there's everything in one big jar file.
The Spheres package is licensed under the GNU General Public License.
Basic class descriptions:
Great Circle intersects Great Circle
Great Circle Arc intersects Great Circle Arc
Great Circle intersects Latitude
Great Circle Arc intersects Latitude Segment
SphericalPolygon contains Point
SphericalPolygon overlaps SphericalPolygon
SphericalPolygon overlaps LatLonBoundingBox
SphericalPolygon overlaps Scene