On Thu, Feb 26, 2009 at 4:26 PM, Barend Gehrels <barend@geodan.nl> wrote:
(source: http://www.opengeospatial.org/standards/sfa#downloads)
I'm talking about OGC more on this list. They have defined a well-defined interface which is followed by the majority of the GIS world and which is based on a mathematical/topological foundation. So we better follow their guidelines than take decisions about every possibility ourselves. Most if not all Open Source implementations are following these rules.
Might I suggest that since you are aiming for OGC compliance, and from your recent mention of including coordinate system projections, that you narrow your library's focus into something more like Boost.GIS instead of Boost.Geometry?
Of course we can concentrate on making polygons "winding-agnostic" and "closing-point-agnostic". I'm not convinced however that that is so easy. If you calculate a convex hull, do you want it returned in the same winding direction as you defined it? It will have an influence, plus a performance malus, on many algorithms. By just providing the "correct" algorithm we enable library users to use our library with every polygon. It cannot be called from the algorithms themselves: to verify the winding rule the area has to be calculated beforehand. This will drastically decrease performance.
The solution might be a traits class telling the winding rule the polygon type has. That might be ever implemented, but for now we'll better concentrate on other things. Same for closing point.
GIS is my work area, so I know it's huge, but it seems like you are trying to tackle GIS + generic geometry library. I don't get the impression that game programmers, for example, will enjoy or use this library. Polygons are not closed (and rarely used, only triangles are) in games, and cannot have holes, and any error checking to determine otherwise is wasteful. Winding is handled by the rendering API, and is also rarely, if ever, checked since the model exporter will have enforced the correct winding. It seems easier to please one group of people (GIS) than to try to please GIS, scientific simulations, game, CAD developers, and more. I believe it will also lead to less discussion about the correctness of interfaces since there is already a standard (OGC) to back you up if you choose GIS. Choose none of them, and you'll have programmers from all industries telling you why your way is wrong and their way is right. --Michael Fawcett P.S. I would love to start using a really fast and elegant Boost.GIS rather than ESRI ArcObjects...