[is_valid] file for is_valid ring implementation (on-going)

include/boost/geometry/algorithms/detail/is_valid/ring.hpp

@@ -0,0 +1,172 @@
+// Boost.Geometry (aka GGL, Generic Geometry Library)
+
+// Copyright (c) 2014, Oracle and/or its affiliates.
+
+// Contributed and/or modified by Menelaos Karavelas, on behalf of Oracle
+
+// Licensed under the Boost Software License version 1.0.
+// http://www.boost.org/users/license.html
+
+#ifndef BOOST_GEOMETRY_ALGORITHMS_DETAIL_IS_VALID_RING_HPP
+#define BOOST_GEOMETRY_ALGORITHMS_DETAIL_IS_VALID_RING_HPP
+
+#include <boost/geometry/core/closure.hpp>
+#include <boost/geometry/core/point_order.hpp>
+
+#include <boost/geometry/algorithms/equals.hpp>
+#include <boost/geometry/algorithms/not_implemented.hpp>
+
+#include <boost/geometry/views/reversible_view.hpp>
+#include <boost/geometry/views/closeable_view.hpp>
+
+#include <boost/geometry/algorithms/detail/is_valid/has_spikes.hpp>
+#include <boost/geometry/algorithms/detail/is_valid/linestring.hpp>
+
+
+namespace boost { namespace geometry
+{
+
+
+#ifndef DOXYGEN_NO_DETAIL
+namespace detail { namespace is_valid
+{
+
+
+// struct to check whether a ring is topologically closed
+template <typename Ring, closure_selector Closure>
+struct is_topologically_closed
+{};
+
+template <typename Ring>
+struct is_topologically_closed<Ring, open>
+{
+    static inline bool apply(Ring const&)
+    {
+        return true;
+    }
+};
+
+template <typename Ring>
+struct is_topologically_closed<Ring, closed>
+{
+    static inline bool apply(Ring const& ring)
+    {
+        return geometry::equals(*boost::begin(ring), *boost::rbegin(ring));
+    }
+};
+
+
+// struct to check if the size is above the minimal one
+// (3 for open, 4 for closed)
+template <typename Ring, closure_selector Closure>
+struct is_below_minimal_size
+{};
+
+template <typename Ring>
+struct is_below_minimal_size<Ring, closed>
+{
+    static inline bool apply(Ring const& ring)
+    {
+        return boost::size(ring) < 4;
+    }
+};
+
+template <typename Ring>
+struct is_below_minimal_size<Ring, open>
+{
+    static inline bool apply(Ring const& ring)
+    {
+        return boost::size(ring) < 3;
+    }
+};
+
+
+
+
+
+
+template
+<
+    typename Ring,
+    order_selector PointOrder,
+    closure_selector Closure
+>
+struct is_valid_ring
+    : not_implemented<Ring>
+{};
+
+
+template <typename Ring, closure_selector Closure>
+struct is_valid_ring<Ring, counterclockwise, Closure>
+{
+    static inline bool apply(Ring const& ring)
+    {
+        typedef typename reversible_view
+            <
+                Ring, iterate_reverse
+            >::type reversible_view_type;
+
+        reversible_view_type reversed_ring(const_cast<Ring&>(ring));
+        return is_valid_ring<Ring, clockwise, Closure>::apply(reversed_ring);
+    }
+};
+
+template <typename Ring, closure_selector Closure>
+struct is_valid_ring<Ring, clockwise, Closure>
+{
+    static inline bool apply(Ring const& ring)
+    {
+        // return invalid if any of the following condition holds:
+        // (a) the ring's size is below the minimal one
+        // (b) the ring has less than three distinct points
+        // (c) the ring is not topologically closed
+        // (d) the ring has spikes
+        //
+        // Note: no need to check if the area is zero. If this is the
+        // case, then the ring must have at least two spikes, which is
+        // checked by condition (d).
+        if ( is_below_minimal_size<Ring, Closure>::apply(ring)
+             || !has_three_distinct_points<Ring>::apply(ring)
+             || !is_topologically_closed<Ring, Closure>::apply(ring)
+             || has_spikes<Ring>::apply(ring) )
+        {
+            return false;
+        }
+
+        // now call self turns to compute self intersections, if any,
+        // and analyze them
+    }
+};
+
+
+}} // namespace dispatch
+#endif // DOXYGEN_NO_DETAIL
+
+
+
+#ifndef DOXYGEN_NO_DISPATCH
+namespace dispatch
+{
+
+// A Ring is a Polygon.
+// A Polygon is always a simple geometric object provided that it is valid.
+//
+// Reference (for polygon validity): OGC 06-103r4 (§6.1.11.1)
+template <typename Ring>
+struct is_valid<Ring, ring_tag>
+    : detail::is_valid::is_valid_ring
+        <
+            Ring,
+            point_order<Ring>::value,
+            closure<Ring>::value
+        >
+{};
+
+
+} // namespace dispatch
+#endif // DOXYGEN_NO_DISPATCH
+
+
+}} // namespace boost::geometry
+
+#endif // BOOST_GEOMETRY_ALGORITHMS_DETAIL_IS_VALID_RING_HPP