From: Andy Little (andy_at_[hidden])
Date: 2003-10-03 10:55:21
Hi, I am a Newbie to Boost :-)
I am currently working on an upgrade to a
point-and-click small wind turbine rotor blade design app,
which involves various physics.
The original did its math in terms of inbuilt types ,
but significant time is spent looking up (say)
whether a length is in metres or millimetres
or an angle in degrees or radians.
I have also had requests from users for ability to work
in (say) feet and inches etc rather than s.i. units.
I have had a look at various physical quantities libraries
including the "quantities" library at boost,
and SIunits at
but they have an odd syntax.
ie both do something like:
length mylength = 20 * metres(); // here length is a type
whereas what would seem to be more useful would be:
metres myLength(20); // here metres is the type
//*1 see footnote on explicit ctor
The critical difference here is that the type is the
unit of dimension, rather than the dimension itself.
As a programmer if I want to know the units
of a variable they are encoded in the type
and if I can't decipher them I can do a conversion:
metres mylength = metres(length_with_unknown_units);
// ok... whatever units length_with_unknown_units was ,
// mylength is its value in metres.
I have spent some time creating a physical_quantities class template,
with this approach, and have put the source code and
a demo programme (and sample output) on my web site at:
I would be interested to hear any views
as to whether this approach is worth pursuing, or suggestions or
( Alternatively there may be a library that does this that I havent found
... ? )
note: I have tried to answer some obvious questions and criticisms
in the Potential FAQ on the page.
--- *1 / this example is actually an error if coded as: metres myLength =1; in my version of physical_quantities because it violates dimensional analysis.
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