"Michael Fawcett" wrote
On 6/9/06, Andy Little wrote:
In cases of vectors, I have only used vectors where all elements are one type of quantity. The vectors are used to represent position, direction and so on in 3 dimensions. A container that holds different quantities I would consider to be a tuple. But I stress I am not an expert.
I am not an expert either, but in practice I have used (incorrectly? should I have used a tuple or a custom data type?) vectors for representing latitude/longitude/altitude with mixed units. Something like vec3<double, unsigned short, double> for decimal degrees, meters, decimal degrees.
Well IMO this sounds more like a navigation coordinate(or whatever is the standard name for it) , and this sounds specific enough to make it its own class, maybe you could convert it to a vector relative to the center of the earth: struct nav_coord{ boost::pqs::angle::s latitude,longtitude; boost::pqs::length::m altitude; operator boost::pqs::three_d::vect<boost::pqs::length::m>(); }; AFAIK a vector classically represents a magnitude and direction without more information though, so the vector would be a position vector
I often need to move back and forth from those units to nautical miles and feet, and I bet a library like PQS would help me out more than meaningful variable names.
You could return the distance (or distance vector) from a distance function (between two navigation coordinates presumably) in (say) meters. In PQS conversions to non-SI units are automatic so the result can be assigned to ( a vector in) nautical miles or feet. (In PQS vectors are designed to work this way as well as scalars) : /* show that conversion works for vectors as well as scalars NB not tested in pqs_3_1_1 release version */ // note:ideally its .. //#include <boost/pqs/three_d/out/vect.hpp> // but in pqs_3_1_1... #include <boost/pqs/three_d/vect_out.hpp> #include <boost/pqs/t1_quantity/types/out/length.hpp> namespace pqs = boost::pqs; int main() { typedef pqs::length::naut_mile naut_mile; typedef pqs::length::ft foot; pqs::three_d::vect<naut_mile> naut_mile_vect( naut_mile(1),naut_mile(1),naut_mile(1) ); pqs::three_d::vect<foot> ft_vect = naut_mile_vect; std::cout << ft_vect <<'\n'; // convert absolute length of vect to meters FWIW pqs::length::m length_of_vect = magnitude(ft_vect); std::cout << length_of_vect <<'\n'; } //output: //[6076.12 ft, 6076.12 ft, 6076.12 ft] //3207.76 m
I am ambivalent about whether the vector should allow mixed data types or not. I could settle for using a tuple instead, as long as vector functions like normalize(my_vec3) or length(my_vec) worked on tuple types as well.
My guess is the nav coordinates would work best as a class? This would enable for example conversion to from position vectors etc as above, which isnt possible with a tuple. regards Andy Little