如何使用boost :: units添加自己的基本单元和转换

#include<boost/units/systems/si/length.hpp>
#include<boost/units/systems/si/time.hpp>
#include<boost/units/systems/si/velocity.hpp>

namespace my_units = boost::units;

typedef my_units::make_base_unit<my_units::length_dimension, 1000>::type my_length_unit;

typedef my_units::scaled_base_unit<my_units::scale<10, my_units::static_rational<-3>>, my_length_unit>::type my_length_unit_in_meters;

my_units::quantity<my_length_unit> length(1.0 * my_length_unit());
my_units::quantity<my_length_unit_in_meters> length_in_meters = length;