Re: [boost] [Review] GGL review starts today, November 5th

Subject: Re: [boost] [Review] GGL review starts today, November 5th
From: Rutger ter Borg (rutger_at_[hidden])
Date: 2009-11-12 02:08:41

Barend Gehrels wrote:

> We've implemented the hull as an "agnostic" strategy because it is not
> dependant on coordinate system itself. It is however dependant on two
> underlying strategies, "side" and "compare". So in cartesian coordinate
> systems the "side" is implemented differently from how it would be
> implemented in a spherical coordinate system. Same for compare
> (spherical compare assumes that the coordinates do not span more than
> halve of the sphere).
> 
> So yes, for points we need to know in which coordinate system they are
> placed, in order to get the calculation strategy. Note that the
> point-type does not have to have one, but the Point Concept. So using a
> traits class you can bind a coordinate system to a point type.
> 
> So if you define a "dictionary coordinate space" where the "side" is
> probably still as defined as it is now for cartesian in the library (it
> can just register the same calculation class), you can call the convex
> hull for it.
> 
> 
> If that answers your question...
> 
> Regards, Barend
> 
> 

Hello Barend,

thanks for the answer. I guess I am being pedantic :-). The name Geometry 
means something like the wikipedia definition for me: 

Geometry is a part of mathematics concerned with questions of size, shape, 
relative position of figures and with properties of space.

A coordinate system is a property of a subset of types of spaces. A 
coordinate system is just a way to express where points are situated in a 
certain space. Distances are properties of a space -- not of a coordinate 
system. 

One of the consequences is that the distance between points in a Euclidean 
space expressed in Cartesian or polar (or ...) coordinate systems are, by 
definition, the same. 

This is probably one of the pieces that is causing my confusion.

Cheers,

Rutger