Using this: #include <boost/geometry/geometry.hpp> #include <iostream> int main() { namespace bg = boost::geometry; // bg = 'B'oost 'G'eometry namespace cs = bg::cs; // cs = 'C'oordinate 'S'ystem typedef bg::model::point<long double, 3, cs::cartesian> CartesianType; CartesianType cartesian(-6.89, -1.61, -1.64); // (theta, phi) typedef bg::model::point<long double, 2, cs::spherical<bg::degree> > SphericalType; SphericalType spherical; bg::strategy::transform::from_cartesian_3_to_spherical_equatorial_2<CartesianType, SphericalType> strategy; bg::transform(cartesian, spherical, strategy); std::cout << "cartesian: " << bg::dsv(cartesian) << std::endl << "spherical: " << bg::dsv(spherical) << std::endl; return 0; } I am getting the second coordinate of 'spherical' equal to 'nan'. I stepped through the Boost code, and got to this in strategy_transform.hpp: template <typename P, typename T> inline bool cartesian_to_spherical_equatorial2(T x, T y, T z, P& p) { assert_dimension<P, 2>(); set_from_radian<0>(p, atan2(y, x)); set_from_radian<1>(p, asin(z)); return true; } Here you see asin(z) . asin() requires the argument to be [-1,1] (http://www.cplusplus.com/reference/clibrary/cmath/asin/). However, this should just be the z component of any Cartesian point right? Is there some restriction on the input Cartesian point to cartesian_to_spherical_equatorial2 (and hence the from_cartesian_3_to_spherical_equatorial_2 strategy)? I see a restriction on from_cartesian_3_to_spherical_polar_2: \note If x,y,z point is not lying on unit sphere, transformation will return false but I don't see the same restriction on from_cartesian_3_to_spherical_equatorial_2. Additionally, it doesn't seem to just be a missing comment because the transform() call actually returns true even though this point is not on the unit sphere. If I normalize the point and call the function: CartesianType cartesian(-0.94862, -0.22167, -0.22580); The conversion seems to work successfully, and the call still returns true. Any thoughts? Is this a bug? If not, why is the function not returning false? And better, shouldn't this condition have at least an assertion (i.e. if the norm != 1, then return false or throw)? Thanks, David