The Spore creatures, likewise, used Metaballs, a geometry creation algorithm that could create smooth tubes along paths in 3D space. Other algorithms for filling spaces and paths are Voronoi patterns, Perlin/Simplex noise, triangulation algorithms, 3D extrusion or rotation, and the Diamond-square algorithm for fractal terrain. These algorithms are particularly well-suited for interactive generators, because the user can provide the input parameters for the generator.