[geos-commits] r3912 - in trunk: include/geos/geom src/geom tests/unit/geom

[svn_geos at osgeo.org]

Author: strk
Date: 2013-08-22 00:07:06 -0700 (Thu, 22 Aug 2013)
New Revision: 3912

Modified:
   trunk/include/geos/geom/Triangle.h
   trunk/src/geom/Triangle.cpp
   trunk/tests/unit/geom/TriangleTest.cpp
Log:
circumcentre() and det() methods added to class Triangle

Includes test for circumcentre()

Contributed by Vishal Tiwari

Modified: trunk/include/geos/geom/Triangle.h
===================================================================
--- trunk/include/geos/geom/Triangle.h	2013-08-22 06:35:35 UTC (rev 3911)
+++ trunk/include/geos/geom/Triangle.h	2013-08-22 07:07:06 UTC (rev 3912)
@@ -47,6 +47,43 @@
 	 * @param resultPoint the point into which to write the inCentre of the triangle
 	 */
 	void inCentre(Coordinate& resultPoint);
+
+	/** 
+	 * Computes the circumcentre of a triangle. The circumcentre is the centre of
+	 * the circumcircle, the smallest circle which encloses the triangle. It is
+	 * also the common intersection point of the perpendicular bisectors of the
+	 * sides of the triangle, and is the only point which has equal distance to
+	 * all three vertices of the triangle.
+	 * <p>
+	 * The circumcentre does not necessarily lie within the triangle. For example,
+	 * the circumcentre of an obtuse isoceles triangle lies outside the triangle.
+	 * <p>
+	 * This method uses an algorithm due to J.R.Shewchuk which uses normalization
+	 * to the origin to improve the accuracy of computation. (See <i>Lecture Notes
+	 * on Geometric Robustness</i>, Jonathan Richard Shewchuk, 1999).
+	 * 
+	 * @param resultPoint the point into which to write the inCentre of the triangle
+	 */
+	void circumcentre(Coordinate& resultPoint);
+
+private:
+
+	/** 
+	 * Computes the determinant of a 2x2 matrix. Uses standard double-precision
+	 * arithmetic, so is susceptible to round-off error.
+	 * 
+	 * @param m00
+	 *          the [0,0] entry of the matrix
+	 * @param m01
+	 *          the [0,1] entry of the matrix
+	 * @param m10
+	 *          the [1,0] entry of the matrix
+	 * @param m11
+	 *          the [1,1] entry of the matrix
+	 * @return the determinant
+	 */
+	double det(double m00 , double m01 , double m10 , double m11) const;
+
 };
 
 

Modified: trunk/src/geom/Triangle.cpp
===================================================================
--- trunk/src/geom/Triangle.cpp	2013-08-22 06:35:35 UTC (rev 3911)
+++ trunk/src/geom/Triangle.cpp	2013-08-22 07:07:06 UTC (rev 3912)
@@ -33,5 +33,30 @@
 	result = Coordinate(inCentreX, inCentreY);
 }
 
+void Triangle::circumcentre(Coordinate& result)
+{
+	double cx = p2.x;
+	double cy = p2.y;
+	double ax = p0.x - cx; 
+	double ay = p0.y - cy; 
+	double bx = p1.x - cx; 
+	double by = p1.y - cy; 
+
+	double denom = 2 * det(ax,ay,bx,by);
+	double numx = det(ay , ax * ax + ay * ay , by , bx * bx + by * by);
+	double numy = det(ax, ax * ax + ay * ay, bx, bx * bx + by * by);
+
+	double ccx = cx - numx / denom;
+	double ccy = cy + numy / denom;
+
+	result = Coordinate(ccx,ccy);
+}
+
+double Triangle::det(double m00 , double m01 , double m10 , double m11) const
+{
+	return m00 * m11 - m01 * m10;
+}
+
+
 } // namespace geos::geom
 } // namespace geos

Modified: trunk/tests/unit/geom/TriangleTest.cpp
===================================================================
--- trunk/tests/unit/geom/TriangleTest.cpp	2013-08-22 06:35:35 UTC (rev 3911)
+++ trunk/tests/unit/geom/TriangleTest.cpp	2013-08-22 07:07:06 UTC (rev 3912)
@@ -117,4 +117,57 @@
 		ensure( center.y < 4.3 );
 		ensure( 0 != ISNAN( center.z ) );
     }
+    // Test circumcentre()
+        template<>
+	template<>
+	void object::test<6>()
+	{   
+		using geos::geom::Triangle;
+		using geos::geom::Coordinate;
+
+		Coordinate x1(5,7);
+		Coordinate x2(6,6);
+		Coordinate x3(2,-2);
+
+		Coordinate y1(3,3);
+		Coordinate y2(9,10);
+		Coordinate y3(6,7);
+
+		Coordinate a1(5,10);
+		Coordinate a2(11,23);
+		Coordinate a3(22,19);
+
+		Triangle t1(x1,x2,x3);
+
+		Triangle t2(y1,y2,y3);
+
+		Triangle t3(a1,a2,a3);
+
+		// For t1:
+		Coordinate c1(0,0);
+		t1.circumcentre(c1);
+		ensure_equals(c1.x ,2 );
+		ensure_equals(c1.y ,3 );
+		ensure( 0 != ISNAN( c1.z ) );
+
+		//For t2:
+		Coordinate c2(0,0);
+		t2.circumcentre(c2);
+		ensure_equals(c2.x ,30.5 );
+		ensure_equals(c2.y ,- 14.5 );
+		ensure( 0 != ISNAN( c2.z ) );
+
+
+		//For t3:
+		Coordinate c3(0,0);
+		t3.circumcentre(c3);
+		ensure( std::fabs(c3.x - 13.0) < 1 );
+		ensure( c3.y > 13.7 );
+		ensure( c3.y < 13.8 );
+		ensure( 0 != ISNAN( c3.z ) );
+		// cout << "CicumCenter of triangle ABC:: " << c1.x << " " << c1.y << endl;
+
+		//  std::cout << "CicumCenter of triangle DEF:: " << c2.x << " " << c2.y << std::endl;
+	}
+
 } // namespace tut