Re: [boost] interest on a geometry library

From: Geoffrey Irving (irving_at_[hidden])
Date: 2006-03-17 13:27:00

On Fri, Mar 17, 2006 at 03:09:26PM -0300, rodolfo_at_[hidden] wrote:
> On Fri, Mar 17, 2006 at 10:17:53AM -0700, Richard Newman wrote:
> > Is it reasonable to extend the logic to check for 3D shapes (i.e., 
> > spheres instead of circles, etc.)?
> > 
> > It certainly would be a reasonable strategy to get the 2D work you have 
> > into the library and treat 3D as a later extension.
> 
> Well, 3D is a whole different beast, and is not implemented yet :) What
> I have is the following (with my name convention, to be changed...):
> 
> geom_t is an abstract base class with basic functions like:
>  - center -> return the center point of the geometry
>  - box -> return a rectangle encompassing the whole geometry
>  - area -> returns its area

It would be better to have a set of nonvirtual classes defining functions
like this inline, and then have a template wrapper class to convert one of
these into a descendant of the virtual class.  This way, someone who wants
to use a million spheres (e.g., for a sphere hierarchy), won't suffer from
virtual function overhead.

> then there's the primitive classes that inherits from geom_t:
>   point_t -> a single point in the 2D space
>   circle_t -> represented as a 2D point and a radius
>   rectangle_t -> represented as two points, the upper left and lower
> 	       right.

You should probably think carefully about which basic types to use here,
especially in terms of small vectors types.  I'm not sure if boost has a
small vector type yet (I didn't see one in uBLAS), but if so it should
definitely be used.

> I'm planning to add polygon and triangle soon.
> 
> There are also operator>> and << to transfer from and to a stream,
> and free functions that returns intersections, unions, etc.
> 
> All coordinates are double. Maybe each primitive should be a template,
> like: point_t<double> is a point with double floating point coordinates, 
> point_t<int> is with integer coordinates, etc.

Templatization of the float type is good, and again point_t should probably
be a general purpose small vector type.

Geoffrey