Projection Traits With Centroid 2 and Determinant 2

Installation/CHANGES.md

@@ -1,6 +1,16 @@
 Release History
 ===============
 
+[Release 5.4](https://github.com/CGAL/cgal/releases/tag/v5.4)
+-----------
+
+Release date: December 2021
+
+### [2D and 3D Linear Geometry Kernel](https://doc.cgal.org/5.4/Manual/packages.html#PkgKernel23)
+
+-   Added `construct_centroid_2_object()` and `compute_determinant_2_object()` in `Projection_traits_xy_3`, `Projection_traits_xz_3`,
+    and`Projection_traits_yz_3` classes.
+
 [Release 5.3](https://github.com/CGAL/cgal/releases/tag/v5.3)
 -----------
 

Kernel_23/include/CGAL/internal/Projection_traits_3.h

@@ -282,6 +282,63 @@ class Squared_distance_projected_3
   }
 };
 
+template <class R,int dim>
+class Construct_centroid_projected_3
+{
+public:
+  typedef typename R::Point_3 Point_3;
+  typedef typename R::Point_2 Point_2;
+  typedef typename R::FT      RT;
+  RT x(const Point_3 &p) const { return Projector<R,dim>::x(p); }
+  RT y(const Point_3 &p) const { return Projector<R,dim>::y(p); }
+
+  Point_2 project(const Point_3& p) const
+  {
+    return Point_2(x(p), y(p));
+  }
+
+  Point_3 embed(const Point_2& p) const
+  {
+    RT coords[3];
+    coords[Projector<R,dim>::x_index] = p.x();
+    coords[Projector<R,dim>::y_index] = p.y();
+    coords[dim] = RT(0);
+
+    return Point_3(coords[0], coords[1], coords[2]);
+  }
+
+  Point_3 operator()(const Point_3& p, const Point_3& q, const Point_3& r) const
+  {
+    const Point_2 p2(project(p));
+    const Point_2 q2(project(q));
+    const Point_2 r2(project(r));
+    return embed(CGAL::centroid(p2, q2, r2));
+  }
+};
+
+template <class R,int dim>
+class Compute_determinant_projected_3
+{
+public:
+  typedef typename R::Vector_3 Vector_3;
+  typedef typename R::Vector_2 Vector_2;
+  typedef typename R::FT       RT;
+  RT x(const Vector_3 &v) const { return Projector<R,dim>::x(v); }
+  RT y(const Vector_3 &v) const { return Projector<R,dim>::y(v); }
+
+  Vector_2 project(const Vector_3& v) const
+  {
+    return Vector_2(x(v), y(v));
+  }
+
+  RT operator()(const Vector_3& v, const Vector_3& w) const
+  {
+    const Vector_2 v2(project(v));
+    const Vector_2 w2(project(w));
+    return CGAL::determinant(v2, w2);
+  }
+};
+
 template <class R,int dim>
 class  Intersect_projected_3
 {
@@ -817,6 +874,9 @@ class Projection_traits_3 {
   typedef Power_side_of_oriented_power_circle_projected_3<Rp, dim> Power_side_of_oriented_power_circle_2;
   typedef Construct_bbox_projected_2<Rp,dim>                  Construct_bbox_2;
 
+  typedef Construct_centroid_projected_3<Rp,dim>              Construct_centroid_2;
+  typedef Compute_determinant_projected_3<Rp,dim>             Compute_determinant_2;
+
   typedef typename Rp::Construct_point_3                      Construct_point_2;
   typedef typename Rp::Construct_weighted_point_3             Construct_weighted_point_2;
   typedef typename Rp::Construct_segment_3                    Construct_segment_2;
@@ -1014,6 +1074,12 @@ class Projection_traits_3 {
   Construct_bbox_2  construct_bbox_2_object() const
     {return Construct_bbox_2();}
 
+  Construct_centroid_2  construct_centroid_2_object() const
+    {return Construct_centroid_2();}
+
+  Compute_determinant_2  compute_determinant_2_object() const
+    {return Compute_determinant_2();}
+
   Compute_scalar_product_2 compute_scalar_product_2_object() const
     {return Compute_scalar_product_2();}
 

Kernel_23/test/Kernel_23/test_projection_traits.cpp

@@ -23,6 +23,14 @@ int main()
 
   K k;
 
+  assert( ( k.construct_centroid_2_object()(p3, q3, r3).x() ==
+            CGAL::centroid(p2, q2, r2).x() ) &&
+          ( k.construct_centroid_2_object()(p3, q3, r3).y() ==
+            CGAL::centroid(p2, q2, r2).y() ) );
+
+  assert( k.compute_determinant_2_object()(v3, w3) ==
+          CGAL::determinant(v2, w2) );
+
   assert( k.compute_scalar_product_2_object()(v3, w3) ==
           v2 * w2 );