Re: [boost] [GTL] - geometric template library - determininginterest

From: Fernando Cacciola (fernando_cacciola_at_[hidden])
Date: 2007-10-08 09:37:50

Hi John,

> I am ready to worry about IF and how boost would accommodate the
> other semantics of a 'point' concept.  As the GTL author seems to
> have pointed out in their explanation of "isotropic", a point is a
> point regardless of its coordinates, and perhaps a point concept
> should involve the coordinate-free operations that make sense on a
> point versus a vector etc., and another concept/term should be
> adopted for the set of coordinates.  If the GTL authors have such
> concepts I am curious to see the interplay of point, vector, and
> coordinate_sets (or whatever they are called).
>
Exacty.
A concept is just a set of minimal requirements. It is not a class,
neither is an adapter (it seems this library somewhat mixes conepts with 
adapters).
So, while we certainly would like one single point class, or at most a few 
of them,
we don't need to use a monolithic super concept.
We can use a set of concepts instead, each one capturing an ortoghonal
aspect of the design.

Off the top of my head:

IndexableCartesian2        (provides indexed access: [0], [1])
IndexableHomogeneous2 (provides indexed access: [0], [1], [2])
Cartesian2                       (provides named access: x(),y())
Homogeneous2               (provides named access: x(),y(),w())

Vector2 (provides coordinate-free vector-specifc operations)
Point2    (provides coordinate-free point-specifc operations)

.. and so on for 3 dimensions, for heteregeneous coordinates, etc.

Notice that a point is a point regardless of its coordinates, and so is a
vector. That is, Vector2/Point2 ARE NOT refinements of the concepts for 
coordinate sets.

Best

Fernando Cacciola