
Geometry : 
Subject: [geometry] nsphere concept
From: Adam Wulkiewicz (adam.wulkiewicz_at_[hidden])
Date: 20130522 13:36:35
Hi,
I have some thoughts about the nsphere that I'd like to share. For now I
think of two changes:
1. The name which I, like the author of comments, find not really
suitable could be changed. I propose to change it to "ball" because:
 in maths it's not only a 3D object, when we consider ndimensional
metric spaces it's ndimensional.
 it is also a name of a nonmath object (e.g. play ball) just like a Box
 it's shorter
2. Currently the implemented model has following template parameters:
template <typename Point, typename Radius>
class nsphere;
Is it really needed to define Radius as a separate type? It might at
least have a default:
template <
typename Point,
typename Radius = coordinate_type<Point>::type
class ball;
Another thing is a separate radius_type but I guess there might be cases
where this is helpful.
3. Access
To get/set radius one may call get_radius<0>(geom) and
set_radius<0>(geom) respectively which is ok since for ellipses and
ellipsoids one must specify radius index.
However I find the centre point access nonintuitive. Correct me if I'm
wrong but it seems that now the nsphere is accessed like a Point? So to
get a centre's cordinate one may call:
get<I>(sph);
which is a little ambiguous.
Why not use an access method already used in the case of the Box  get
with index? Like this:
get<centre, I>(sph)
get<radius, I>(sph)
The first one would return coordinate_type and the second one
radius_type which could be different.
What do you think?
Regards,
Adam
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