Package org.hipparchus.geometry.spherical.twod

Class SphericalPolygonsSet

    • Constructor Detail

      • SphericalPolygonsSet

        public SphericalPolygonsSet​(Vector3D center,
                            Vector3D meridian,
                            double outsideRadius,
                            int n,
                            double tolerance)
                     throws MathIllegalArgumentException
        Build a polygons set representing a regular polygon.
        Parameters:
        center - center of the polygon (the center is in the inside half)
        meridian - point defining the reference meridian for first polygon vertex
        outsideRadius - distance of the vertices to the center
        n - number of sides of the polygon
        tolerance - below which points are consider to be identical
        Throws:
        MathIllegalArgumentException - if tolerance is smaller than Sphere1D.SMALLEST_TOLERANCE

      • SphericalPolygonsSet

        public SphericalPolygonsSet​(BSPTree<Sphere2D> tree,
                            double tolerance)
                     throws MathIllegalArgumentException
        Build a polygons set from a BSP tree.

        The leaf nodes of the BSP tree must have a Boolean attribute representing the inside status of the corresponding cell (true for inside cells, false for outside cells). In order to avoid building too many small objects, it is recommended to use the predefined constants Boolean.TRUE and Boolean.FALSE

        Parameters:
        tree - inside/outside BSP tree representing the region
        tolerance - below which points are consider to be identical
        Throws:
        MathIllegalArgumentException - if tolerance is smaller than Sphere1D.SMALLEST_TOLERANCE

      • SphericalPolygonsSet

        public SphericalPolygonsSet​(Collection<SubHyperplane<Sphere2D>> boundary,
                            double tolerance)
                     throws MathIllegalArgumentException
        Build a polygons set from a Boundary REPresentation (B-rep).

        The boundary is provided as a collection of sub-hyperplanes. Each sub-hyperplane has the interior part of the region on its minus side and the exterior on its plus side.

        The boundary elements can be in any order, and can form several non-connected sets (like for example polygons with holes or a set of disjoint polygons considered as a whole). In fact, the elements do not even need to be connected together (their topological connections are not used here). However, if the boundary does not really separate an inside open from an outside open (open having here its topological meaning), then subsequent calls to the checkPoint method will not be meaningful anymore.

        If the boundary is empty, the region will represent the whole space.

        Parameters:
        boundary - collection of boundary elements, as a collection of SubHyperplane objects
        tolerance - below which points are consider to be identical
        Throws:
        MathIllegalArgumentException - if tolerance is smaller than Sphere1D.SMALLEST_TOLERANCE

      • SphericalPolygonsSet

        public SphericalPolygonsSet​(double hyperplaneThickness,
                            S2Point... vertices)
                     throws MathIllegalArgumentException
        Build a polygon from a simple list of vertices.

        The boundary is provided as a list of points considering to represent the vertices of a simple loop. The interior part of the region is on the left side of this path and the exterior is on its right side.

        This constructor does not handle polygons with a boundary forming several disconnected paths (such as polygons with holes).

        For cases where this simple constructor applies, it is expected to be numerically more robust than the general constructor using subhyperplanes.

        If the list is empty, the region will represent the whole space.

        This constructor assumes that edges between vertices, including the edge between the last and the first vertex, are shorter than pi. If edges longer than pi are used it may produce unintuitive results, such as reversing the direction of the edge. This implies using a vertices array of length 1 or 2 in this constructor produces an ill-defined region. Use one of the other constructors or RegionFactory instead.

        The list of vertices is reduced by selecting a sub-set of vertices before creating the boundary set. Every point in vertices will be on the boundary of the constructed polygon set, but not necessarily the center-line of the boundary.

        Polygons with thin pikes or dents are inherently difficult to handle because they involve circles with almost opposite directions at some vertices. Polygons whose vertices come from some physical measurement with noise are also difficult because an edge that should be straight may be broken in lots of different pieces with almost equal directions. In both cases, computing the circles intersections is not numerically robust due to the almost 0 or almost π angle. Such cases need to carefully adjust the hyperplaneThickness parameter. A too small value would often lead to completely wrong polygons with large area wrongly identified as inside or outside. Large values are often much safer. As a rule of thumb, a value slightly below the size of the most accurate detail needed is a good value for the hyperplaneThickness parameter.

        Parameters:
        hyperplaneThickness - tolerance below which points are considered to belong to the hyperplane (which is therefore more a slab). Should be greater than FastMath.ulp(4 * FastMath.PI) for meaningful results.
        vertices - vertices of the simple loop boundary
        Throws:
        MathIllegalArgumentException - if tolerance is smaller than Sphere1D.SMALLEST_TOLERANCE
        MathRuntimeException - if vertices contains only a single vertex or repeated vertices.

    • Method Detail

      • buildNew

        public SphericalPolygonsSet buildNew​(BSPTree<Sphere2D> tree)
        Build a region using the instance as a prototype.

        This method allow to create new instances without knowing exactly the type of the region. It is an application of the prototype design pattern.

        The leaf nodes of the BSP tree must have a Boolean attribute representing the inside status of the corresponding cell (true for inside cells, false for outside cells). In order to avoid building too many small objects, it is recommended to use the predefined constants Boolean.TRUE and Boolean.FALSE. The tree also must have either null internal nodes or internal nodes representing the boundary as specified in the getTree method).

        Specified by:
        buildNew in interface Region<Sphere2D>
        Specified by:
        buildNew in class AbstractRegion<Sphere2D,​Sphere1D>
        Parameters:
        tree - inside/outside BSP tree representing the new region
        Returns:
        the built region

      • getBoundaryLoops

        public List<Vertex> getBoundaryLoops()
                              throws MathIllegalStateException
        Get the boundary loops of the polygon.

        The polygon boundary can be represented as a list of closed loops, each loop being given by exactly one of its vertices. From each loop start vertex, one can follow the loop by finding the outgoing edge, then the end vertex, then the next outgoing edge ... until the start vertex of the loop (exactly the same instance) is found again once the full loop has been visited.

        If the polygon has no boundary at all, a zero length loop array will be returned.

        If the polygon is a simple one-piece polygon, then the returned array will contain a single vertex.

        All edges in the various loops have the inside of the region on their left side (i.e. toward their pole) and the outside on their right side (i.e. away from their pole) when moving in the underlying circle direction. This means that the closed loops obey the direct trigonometric orientation.

        Returns:
        boundary of the polygon, organized as an unmodifiable list of loops start vertices.
        Throws:
        MathIllegalStateException - if the tolerance setting does not allow to build a clean non-ambiguous boundary
        See Also:
        Vertex, Edge

      • getEnclosingCap

        public EnclosingBall<Sphere2D,​S2Point> getEnclosingCap()
        Get a spherical cap enclosing the polygon.

        This method is intended as a first test to quickly identify points that are guaranteed to be outside of the region, hence performing a full checkPoint only if the point status remains undecided after the quick check. It is is therefore mostly useful to speed up computation for small polygons with complex shapes (say a country boundary on Earth), as the spherical cap will be small and hence will reliably identify a large part of the sphere as outside, whereas the full check can be more computing intensive. A typical use case is therefore: 

           // compute region, plus an enclosing spherical cap
   SphericalPolygonsSet complexShape = ...;
   EnclosingBall<Sphere2D, S2Point> cap = complexShape.getEnclosingCap();

   // check lots of points
   for (Vector3D p : points) {

     final Location l;
     if (cap.contains(p)) {
       // we cannot be sure where the point is
       // we need to perform the full computation
       l = complexShape.checkPoint(v);
     } else {
       // no need to do further computation,
       // we already know the point is outside
       l = Location.OUTSIDE;
     }

     // use l ...

   }

        In the special cases of empty or whole sphere polygons, special spherical caps are returned, with angular radius set to negative or positive infinity so the ball.contains(point) method return always false or true.

        This method is not guaranteed to return the smallest enclosing cap.

        Returns:
        a spherical cap enclosing the polygon