Consequently, there have been many proposed methods for three-dimensional coordinate generation, including rule-based, fragment-based , and distance geometry embedding methods . There are a few free or open source packages capable of coordinatte generation, including BALL , FROG , RDKit , and Open Babel . The latter, which is highly popular, has used a rule-based coordinate builder with a small set of ring fragments, followed by force field minimization. Fragment-based approaches have reported increased accuracy and speed over Open Babel, since no force field minimization is required.