Re: [boost] Geometry/Vector Lib

From: james.jones_at_[hidden]
Date: 2006-09-20 17:06:10

From: "Olivier Grant" <olivier.grant_at_[hidden]>
On 9/20/06, Walter Landry <wlandry_at_[hidden]> wrote:
> > This seems wrong.  If I want to add a vector2d to a vector3d, then I
> > should have to do it manually.  Otherwise, it should be a type error.
> 
> it depends how you see the problem I suppose. A 2D vector is just a 3D
> vector with z == 0. A 3D vector is a 4D vector with w == 1. And so on by
> extension. Since these vector classes are not supposed to be used in a
> polymorphic way, each argument of a function call is well-known by the user
> - or at least should be :) - so I would not raise an exception in the case
> of the use of two vectors with different dimensions.

But a 2D vector is NOT just a 3D vector with z = 0!! It might sit in a subspace of a 3D vector space, but not necessarily in the z=0 plane. It could just as easily be a 2D vector in the x - 2y + 3z = 0 plane.

Certainly do it this way if you want to - maybe it makes perfect sense for your particular application. But I'd never want to see something like this standardized in BOOST. It just ain't right. :)

Also, if a 2D vector is a 3D vector with z=0, and a 3D vector is a 4D vector with w=1, "and so on by extension", then how would a 4D vector compare with a 5D vector? I don't get the extension. When you first posted your example, I assumed you'd made a typo when you set w=1, but now I think you did that on purpose. Why wouldn't w=0?

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