-------------------------------------------------- From: "Bruno Lalande" <bruno.lalande@gmail.com> Sent: Thursday, October 09, 2008 9:51 AM To: <boost@lists.boost.org> Subject: Re: [boost] Geometry and spatial indexes, my opinion
Actually in the library I've been working on the definition of the point type is of lesser importance. All of my algorithms are designed to access point coordinates via a traits specialization which details how the point's coordinates are accessed. It works like this (please excuse email formatting :)
As said several times by several people including me, it's exactly what everybody out there is doing. There's nothing fundamentally new in what you propose and in the code you just pasted.
The library I've written is the only one in the vault which uses this mechanism. Your library in the vault directly accesses the interfaces for the underlying points, segments and polygons: Point: (from intersection_linestring.hpp) bool clip_segment( const box<PB>& b, segment<PS>& s, bool& sp1_clipped, bool& sp2_clipped) const { typedef typename select_type_traits < typename PB::coordinate_type, typename PS::coordinate_type
::type T; double t1 = 0; double t2 = 1; T dx = s.second.x() - s.first.x();///Segment type directly accessed followed by call to point interfaces .x()/.y() T dy = s.second.y() - s.first.y(); T p1 = -dx; T p2 = dx; T p3 = -dy; T p4 = dy; T q1 = s.first.x() - b.min().x(); T q2 = b.max().x() - s.first.x(); T q3 = s.first.y() - b.min().y(); T q4 = b.max().y() - s.first.y(); ...
Polygon: /*! \brief Centroid of a polygon. \note Because outer ring is clockwise, inners are counter clockwise, triangle approach is OK and works for polygons with rings. */ template<typename P, typename Y, typename S> inline void centroid_polygon(const Y& poly, P& c, const S& strategy) { if (ring_ok(poly.outer(), c)) { typename S::state_type state; loop(poly.outer(), strategy, state);//These calls directly access the specified type in Y. for (typename Y::inner_container_type::const_iterator it = poly.inners().begin(); it != poly.inners().end(); it++) { loop(*it, strategy, state); } state.centroid(c); } } This is very different from what I have put up on the vault. I do not understand why you don't see this. This code requires the user to either wrap their types in an adaptor or translate them into a type which supports the interface required by your algorithm implementations. I have looked through a lot of this code and it just doesn't do what I am describing. Your algorithms here require your points to have x() and y() defined. The segment must have first/second for the point access, and the polygon has to have outer()/inner().
That's precisely why I've just said (like you) that the definition of a point type in not really important.
I agree that it isn't important, but I don't see how your algorithms will work with the fusion example I have put up.
Bruno
Sincerely, Brandon
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