Mapx is a coordinate transformation library developed at NSIDC. The C code was initially developed from equations given by Snyder (1982) and tested against the examples in his Appendix A. Additional projections have been added as needed. The C version of Mapx currently supports 11 common projections, in both spherical and ellipsoid forms when appropriate.
The Java version was ported from the C to simplify using the transforms in Java applets and applications. The Java lags behind the C somewhat and currently supports nine common projections, in both spherical and ellipsoid forms when appropriate.