Re: [Boost-users] boost::units - converting from one derived_dimension to another across systems (imperial to metric)

AMDG On 11/19/2018 09:09 PM, Matt Vinson via Boost-users wrote:

Eisuke Kawashima: Thank You.  I'll have a look.  When I saw Boost.Units did not have imperial and we had to create it ourselves, I thought: the US is s 5 trillion dollar market, most of those markets need programming, all are on imperial.  Boost.Units needs imperial and programmers would find and use it.

Steven Watanabe:  Thank You.  This solution doesn't seem correct as it does not consider "length"....

How is it wrong? length cancels out. The divides version will give exactly the same type.

boost::units::derived_dimension<   boost::units::mass_base_dimension, 1,   boost::units::time_base_dimension, -2>::typeI thought I'd at it (L M T^-2 L-1) but this didn't do well.:        typedef boost::units::derived_dimension<             boost::units::length_base_dimension, 1,             boost::units::mass_base_dimension, 1,             boost::units::time_base_dimension, -2,             boost::units::length_base_dimension, -1         >::type             lineal_force_dimension;

derived_dimension can't handle multiple uses of the same base dimension. Even if it did, it would just cancel them out, so this serves to purpose.

So, I tried the " typedef boost::mpl::divides<...>" solution as it has force and length.  I am closer, I hope. *.h------------------------------------------------------------------------------------------------------------------------------------------ namespace dimensional_analysis {       typedef boost::units::length_base_dimension::dimension_type length_dimension;       typedef boost::units::mass_base_dimension::dimension_type mass_dimension;

      typedef boost::units::make_system<             boost::units::us::inch_base_unit,             boost::units::us::pound_base_unit         >::type ip_system;

    namespace lineal_force {         typedef boost::mpl::divides<             boost::units::force_dimension,             boost::units::length_dimension>::type             lineal_force_dimension;         namespace imperial {             typedef boost::units::unit<                 lineal_force_dimension,                 dimensional_analysis ::ip_system             > lineal_force_unit;             typedef boost::units::quantity pound_per_in_quantity;             BOOST_UNITS_STATIC_CONSTANT(pound_per_inch, pound_per_in_quantity);         }         namespace si {             typedef boost::units::unit<                 lineal_force_dimension,                 boost::units::si::system             > lineal_force_unit;

This is not the unit you want. The SI unit of force is N, not kg. kilogram-force is not currently provided by Boost.Units and you'll need to define it yourself. (As in your previous post.)

            typedef boost::units::quantity kg_per_meter_quantity;             BOOST_UNITS_STATIC_CONSTANT(kg_per_meter, kg_per_meter_quantity);         }     }//lineal_force }//dimensional_analysis <snip>

In Christ, Steven Watanabe