Package com.google.common.geometry

Class S2EdgeUtil.EdgeCrosser

java.lang.Object
com.google.common.geometry.S2EdgeUtil.EdgeCrosser
Enclosing class:
S2EdgeUtil
public static final class S2EdgeUtil.EdgeCrosser extends Object
Used to efficiently test a fixed edge AB against an edge chain. To use it, initialize with the edge AB, and call robustCrossing(S2Point, S2Point) or edgeOrVertexCrossing(S2Point, S2Point) with each edge of the chain.

This class is not thread-safe.

  • Field Details

    • a

      private S2Point a

    • b

      private S2Point b

    • aCrossB

      private S2Point aCrossB

    • c

      private S2Point c
      Previous vertex in the vertex chain.

    • acb

      private int acb
      The orientation of the triangle ACB, i.e. the orientation around the current vertex.

    • bdaReturn

      int bdaReturn
      The orientation of triangle BDA. This is used to return an extra value from robustCrossingInternal().

    • hasTangents

      private boolean hasTangents
      True if the tangents have been computed. To reduce the number of calls to S2Predicates.Sign.expensive(com.google.common.geometry.S2Point, com.google.common.geometry.S2Point, com.google.common.geometry.S2Point, boolean), we compute an outward-facing tangent at A and B if necessary. If the plane perpendicular to one of these tangents separates AB from CD (i.e., one edge on each side) then there is no intersection.

    • aTangent

      private S2Point aTangent
      Outward-facing tangent at A.

    • bTangent

      private S2Point bTangent
      Outward-facing tangent at B.

  • Constructor Details

    • EdgeCrosser

      public EdgeCrosser()
      Constructs an uninitialized edge crosser. Invoke init(S2Point, S2Point) before calling the other methods.

    • EdgeCrosser

      public EdgeCrosser(S2Point a, S2Point b)
      Convenience constructor that calls init() with the given fixed edge AB.

    • EdgeCrosser

      public EdgeCrosser(S2Point a, S2Point b, S2Point c)
      AB is the given fixed edge, and C is the first vertex of the vertex chain. Equivalent to using the two-arg constructor and calling restartAt(c).

  • Method Details

    • init

      public void init(S2Point a, S2Point b)

    • restartAt

      public void restartAt(S2Point c)
      Call this method when your chain 'jumps' to a new place.

    • triage

      static int triage(S2Point ab, S2Point c)
      Returns the sign of the determinant of the column matrix ABC, given the precomputed cross product AB.

    • robustCrossing

      public int robustCrossing(S2Point d)
      This method is equivalent to calling the robustCrossing(com.google.common.geometry.S2Point) function (defined below) on the edges AB and CD. It returns +1 if there is a crossing, -1 if there is no crossing, and 0 if two points from different edges are the same. Returns 0 or -1 if either edge is degenerate. As a side effect, it saves vertex D to be used as the next vertex C.

    • robustCrossing

      public int robustCrossing(S2Point c, S2Point d)
      As robustCrossing(S2Point), but restarts at c if that is not the previous endpoint.

    • edgeOrVertexCrossing

      public boolean edgeOrVertexCrossing(S2Point d)
      This method is equivalent to the edgeOrVertexCrossing(com.google.common.geometry.S2Point) method defined below. It is similar to robustCrossing(com.google.common.geometry.S2Point), but handles cases where two vertices are identical in a way that makes it easy to implement point-in-polygon containment tests.

    • edgeOrVertexCrossing

      public boolean edgeOrVertexCrossing(S2Point c, S2Point d)
      As edgeOrVertexCrossing(S2Point), but restarts at c if that is not the previous endpoint.

    • robustCrossingInternal

      private int robustCrossingInternal(S2Point d)
      Compute the actual result, and then save the current vertex D as the next vertex C, and save the orientation of the next triangle ACB (which is opposite to the current triangle BDA).

    • robustCrossingInternal2

      private int robustCrossingInternal2(S2Point d)

    • sign

      private static int sign(S2Point a, S2Point b, S2Point c, S2Point aCrossB)
      Helper that checks the sign of ABC, using a precomputed cross product for AxB.