Class Orientation

java.lang.Object
org.locationtech.jts.algorithm.Orientation

public class Orientation extends Object
Functions to compute the orientation of basic geometric structures including point triplets (triangles) and rings. Orientation is a fundamental property of planar geometries (and more generally geometry on two-dimensional manifolds).

Determining triangle orientation is notoriously subject to numerical precision errors in the case of collinear or nearly collinear points. JTS uses extended-precision arithmetic to increase the robustness of the computation.

Author:
Martin Davis
  • Field Summary

    Fields
    Modifier and Type
    Field
    Description
    static final int
    A value that indicates an orientation of clockwise, or a right turn.
    static final int
    A value that indicates an orientation of collinear, or no turn (straight).
    static final int
    A value that indicates an orientation of counterclockwise, or a left turn.
    static final int
    A value that indicates an orientation of counterclockwise, or a left turn.
    static final int
    A value that indicates an orientation of clockwise, or a right turn.
    static final int
    A value that indicates an orientation of collinear, or no turn (straight).
  • Constructor Summary

    Constructors
    Constructor
    Description
     
  • Method Summary

    Modifier and Type
    Method
    Description
    static int
    Returns the orientation index of the direction of the point q relative to a directed infinite line specified by p1-p2.
    static boolean
    isCCW(Coordinate[] ring)
    Tests if a ring defined by an array of Coordinates is oriented counter-clockwise.
    static boolean
    Tests if a ring defined by a CoordinateSequence is oriented counter-clockwise.
    static boolean
    Tests if a ring defined by an array of Coordinates is oriented counter-clockwise, using the signed area of the ring.

    Methods inherited from class java.lang.Object

    equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
  • Field Details

    • CLOCKWISE

      public static final int CLOCKWISE
      A value that indicates an orientation of clockwise, or a right turn.
      See Also:
    • COUNTERCLOCKWISE

      public static final int COUNTERCLOCKWISE
      A value that indicates an orientation of counterclockwise, or a left turn.
      See Also:
    • LEFT

      public static final int LEFT
      A value that indicates an orientation of counterclockwise, or a left turn.
      See Also:
    • COLLINEAR

      public static final int COLLINEAR
      A value that indicates an orientation of collinear, or no turn (straight).
      See Also:
    • STRAIGHT

      public static final int STRAIGHT
      A value that indicates an orientation of collinear, or no turn (straight).
      See Also:
  • Constructor Details

    • Orientation

      public Orientation()
  • Method Details

    • index

      public static int index(Coordinate p1, Coordinate p2, Coordinate q)
      Returns the orientation index of the direction of the point q relative to a directed infinite line specified by p1-p2. The index indicates whether the point lies to the LEFT or RIGHT of the line, or lies on it COLLINEAR. The index also indicates the orientation of the triangle formed by the three points ( COUNTERCLOCKWISE, CLOCKWISE, or STRAIGHT )
      Parameters:
      p1 - the origin point of the line vector
      p2 - the final point of the line vector
      q - the point to compute the direction to
      Returns:
      -1 ( CLOCKWISE or RIGHT ) if q is clockwise (right) from p1-p2; 1 ( COUNTERCLOCKWISE or LEFT ) if q is counter-clockwise (left) from p1-p2; 0 ( COLLINEAR or STRAIGHT ) if q is collinear with p1-p2
    • isCCW

      public static boolean isCCW(Coordinate[] ring)
      Tests if a ring defined by an array of Coordinates is oriented counter-clockwise.
      • The list of points is assumed to have the first and last points equal.
      • This handles coordinate lists which contain repeated points.
      • This handles rings which contain collapsed segments (in particular, along the top of the ring).
      This algorithm is guaranteed to work with valid rings. It also works with "mildly invalid" rings which contain collapsed (coincident) flat segments along the top of the ring. If the ring is "more" invalid (e.g. self-crosses or touches), the computed result may not be correct.
      Parameters:
      ring - an array of Coordinates forming a ring (with first and last point identical)
      Returns:
      true if the ring is oriented counter-clockwise.
      Throws:
      IllegalArgumentException - if there are too few points to determine orientation (< 4)
    • isCCW

      public static boolean isCCW(CoordinateSequence ring)
      Tests if a ring defined by a CoordinateSequence is oriented counter-clockwise.
      • The list of points is assumed to have the first and last points equal.
      • This handles coordinate lists which contain repeated points.
      • This handles rings which contain collapsed segments (in particular, along the top of the ring).
      This algorithm is guaranteed to work with valid rings. It also works with "mildly invalid" rings which contain collapsed (coincident) flat segments along the top of the ring. If the ring is "more" invalid (e.g. self-crosses or touches), the computed result may not be correct.
      Parameters:
      ring - a CoordinateSequence forming a ring (with first and last point identical)
      Returns:
      true if the ring is oriented counter-clockwise.
    • isCCWArea

      public static boolean isCCWArea(Coordinate[] ring)
      Tests if a ring defined by an array of Coordinates is oriented counter-clockwise, using the signed area of the ring.
      • The list of points is assumed to have the first and last points equal.
      • This handles coordinate lists which contain repeated points.
      • This handles rings which contain collapsed segments (in particular, along the top of the ring).
      • This handles rings which are invalid due to self-intersection
      This algorithm is guaranteed to work with valid rings. For invalid rings (containing self-intersections), the algorithm determines the orientation of the largest enclosed area (including overlaps). This provides a more useful result in some situations, such as buffering.

      However, this approach may be less accurate in the case of rings with almost zero area. (Note that the orientation of rings with zero area is essentially undefined, and hence non-deterministic.)

      Parameters:
      ring - an array of Coordinates forming a ring (with first and last point identical)
      Returns:
      true if the ring is oriented counter-clockwise.