Re: [Boost-users] [units][geometry] subtract_typeof_helper<> help!

Hi Alfredo,

Great, please keep me (us) posted

Actually the timing is convenient because this indeed was still an action to be taken, mentioned in the review report.

What I have so far is for example using namespace boost::geometry; using namespace boost::units; model::pointsi::length > p1(1.*si::meter,2.*si::meter,3.*si::meter); std::clog << distance(p1,p1) << std::endl; // outputs 0. * meter

This does not work for me. The type declaration works, but coordinates are still doubles here. The construction effectively translates to "double d = 1.*si::meter". This gives me the message "cannot convert from 'boost::units::quantity<Unit>' to 'double'". So how does this work for you?

#include ... using namespace boost::units; boost::arraysi::length, 3> p5={{10.*si::meter,11.*si::meter,12.*si::meter}}; std::clog << distance(p5,p5) << std::endl; //outputs 0. * meter

Construction works here for me, but calculating distance does not. Because distance behind the screens takes the square root, after squaring. This requires thorough integration with Boost.Units at those places, which is not planned.

the implementation I have is very primitive and it is practically a mockup because it bypasses most of the features of the Boost.Geometry library; mainly because I didn't understand them internally.

So Boost.Geometry is not dependant on Boost.Units. I think the way to go is define a point type using a coordinate system using Boost.Units, like you did, and also add quantities there. I just tried that. However, the output is then still in values, so distance will result a value (e.g. double). It runs like this: // Note that the last 3 template parameters have defaults typedef model::quantity_pointsi::length > point; point p1(1 * meter, 2 * meter); // only quantities expected point p2(3 * meter, 4 * meter); quantitysi::length d = distance(p1, p2) * si::meter; Then it IS possible to create a set of overloaded functions, e.g. boost::geometry::units::set(point, quantity) to set it from a quantity boost::geometry::units::get(point) to return a quantity boost::geometry::units::distance(a,b) -> returns a quantity in the coordinate dimensions from the measured distance boost::geometry::units::area(a) -> returns a quantity e.g. in square_meters from a polygon So I added two of these functions as well, giving: std::cout << units::get<0>(p2) << std::endl; quantitysi::length d = units::distance(p1, p2); std::cout << d << std::endl; reporting all quantities including units. It required some small additional metafunctions as well. I just committed it, for the moment as a new example (including definitions), here: http://bit.ly/dEip8s Regards, Barend