### [3D Alpha Wrapping (new package)](https://doc.cgal.org/5.5/Manual/packages.html#PkgAlphaWrap3)
- Added the cmake target `CGAL::CGAL_Basic_viewer` to ease the compilation of programs using the basic viewer-based function `CGAL::draw()`. This target will define the macro and link with `CGAL_Qt5` target when linked with it.
- This component takes a 3D triangle mesh, soup, or point set as input, and generates a valid (watertight, intersection-free, and combinatorially 2-manifold) surface triangle mesh that contains the input.
The algorithm proceeds by shrink-wrapping and refining a 3D Delaunay triangulation, starting from a loose bounding box of the input.
Two user-defined parameters, alpha and offset, offer control over the maximum size of cavities where the shrink-wrapping process can enter, and the tightness of the final surface mesh to the input, respectively. Once combined, these parameters provide a means to trade fidelity
to the input for complexity of the output.
- The kernel providing exact constructions and exact predicates ([`CGAL::Exact_predicates_exact_constructions_kernel`](https://doc.cgal.org/5.4/Kernel_23/classCGAL_1_1Exact__predicates__exact__constructions__kernel.html)) is now thread-safe. See changes in `2D and 3D Linear Geometry Kernel` for more details.
See also the [announcement page](https://www.cgal.org/2022/05/18/alpha_wrap/).
- The class `Geomview_stream` and all the dependent features have been removed from CGAL. Those features were actually no longer supported since CGAL-5.3 but it was not properly announced.
### [Shape Regularization](https://doc.cgal.org/5.4/Manual/packages.html#PkgShapeRegularization) (new package)
- Added an [overload of the function `CGAL::convex_hull_3()`](https://doc.cgal.org/5.5/Convex_hull_3/group__PkgConvexHull3Functions.html#ga52fca4745c2ef0351063fbe66b035fd1), which writes the result in an indexed triangle set.
- This package enables to regularize a set of segments and open or closed contours in 2D and a set of planes in 3D such that all input objects are rotated and aligned with respect to the user-specified conditions. In addition, it provides a global regularization framework that can be adjusted for the user needs and any type of geometric objects.
### [Weights](https://doc.cgal.org/5.4/Manual/packages.html#PkgWeights) (new package)
- Add vertex, edge, and hole ranges.
- The concept [`GeneralPolygonWithHoles_2`](https://doc.cgal.org/5.5/Polygon/classGeneralPolygonWithHoles__2.html) now requires the nested type `Polygon_2` instead of `General_polygon_2`.
- This package provides a simple and unified interface to different types of weights. In particular, it groups all weights into three category: analytic weights including all basic weights which can be computed analytically for a query point with respect to its local neighbors in 2D and 3D; barycentric weights, including all weights which can be computed for a query point with respect to the vertices of a planar polygon; and weighting regions, including all weights which are used to balance other weights.
- The concept [`GeneralPolygonSetTraits_2`](https://doc.cgal.org/5.5/Boolean_set_operations_2/classGeneralPolygonSetTraits__2.html) now requires the nested type `Construct_polygon_with_holes_2` instead of `Construct_general_polygon_with_holes_2`.
- **Breaking change**: The headers `Segment_coordinates_2.h` and `Triangle_coordinates_2.h` are renamed to `segment_coordinates_2.h` and `triangle_coordinates_2.h`.
- Removed old code deprecated in CGAL 4.9 and 4.10 (global functions, and information associated with darts).
- The classes [`Segment_coordinates_2`](https://doc.cgal.org/5.4/Barycentric_coordinates_2/classCGAL_1_1Barycentric__coordinates_1_1Segment__coordinates__2.html) and [`Triangle_coordinates_2`](https://doc.cgal.org/5.4/Barycentric_coordinates_2/classCGAL_1_1Barycentric__coordinates_1_1Triangle__coordinates__2.html) are deprecated. The free functions [`compute_segment_coordinates_2()`](https://doc.cgal.org/5.4/Barycentric_coordinates_2/classCGAL_1_1Barycentric__coordinates_1_1Segment__coordinates__2.html#a134d363dccaeecb5621fa608fac76eaf) and [`compute_triangle_coordinates_2()`](https://doc.cgal.org/5.4/Barycentric_coordinates_2/classCGAL_1_1Barycentric__coordinates_1_1Triangle__coordinates__2.html#a958fee3ad9613d7bfa9d7a976aa3548f) are deprecated as well. Instead, the free functions [`segment_coordinates_2()`](https://doc.cgal.org/5.4/Barycentric_coordinates_2/group__PkgBarycentricCoordinates2RefFunctions.html#gab856ca68d37f58e6cdf74c8aac6f4245) and [`triangle_coordinates_2()`](https://doc.cgal.org/5.4/Barycentric_coordinates_2/group__PkgBarycentricCoordinates2RefFunctions.html#gaa378786f8996dbcefe7923ebb711e4dd) should be used.
- The enums [`Query_point_location`](https://doc.cgal.org/5.4/Barycentric_coordinates_2/namespaceCGAL_1_1Barycentric__coordinates.html#aedeeb072a2024053a016afd15e591331) and [`Type_of_algorithm`](https://doc.cgal.org/5.4/Barycentric_coordinates_2/namespaceCGAL_1_1Barycentric__coordinates.html#a5e5682512438422f23d6080edc49c05b) are deprecated. Instead, the enum [`Computation_policy_2`](https://doc.cgal.org/5.4/Barycentric_coordinates_2/namespaceCGAL_1_1Barycentric__coordinates.html#a478bbcec416216b2274ee4b4e97b0e6c) should be used.
- The classes [`Wachspress_2`](https://doc.cgal.org/5.4/Barycentric_coordinates_2/classCGAL_1_1Barycentric__coordinates_1_1Wachspress__2.html), [`Discrete_harmonic_2`](https://doc.cgal.org/5.4/Barycentric_coordinates_2/classCGAL_1_1Barycentric__coordinates_1_1Discrete__harmonic__2.html), [`Mean_value_2`](https://doc.cgal.org/5.4/Barycentric_coordinates_2/classCGAL_1_1Barycentric__coordinates_1_1Mean__value__2.html), and [`Generalized_barycentric_coordinates_2`](https://doc.cgal.org/5.4/Barycentric_coordinates_2/classCGAL_1_1Barycentric__coordinates_1_1Generalized__barycentric__coordinates__2.html) are deprecated. As consequence, the concept [`BarycentricCoordinates_2`](https://doc.cgal.org/5.4/Barycentric_coordinates_2/classCGAL_1_1Barycentric__coordinates_1_1BarycentricCoordinates__2.html) is deprecated as well. Instead, the classes [`Wachspress_coordinates_2`](https://doc.cgal.org/5.4/Barycentric_coordinates_2/classCGAL_1_1Barycentric__coordinates_1_1Wachspress__coordinates__2.html), [`Discrete_harmonic_coordinates_2`](https://doc.cgal.org/5.4/Barycentric_coordinates_2/classCGAL_1_1Barycentric__coordinates_1_1Discrete__harmonic__coordinates__2.html), and [`Mean_value_coordinates_2`](https://doc.cgal.org/5.4/Barycentric_coordinates_2/classCGAL_1_1Barycentric__coordinates_1_1Mean__value__coordinates__2.html) should be used.
- Added the class [`Harmonic_coordinates_2`](https://doc.cgal.org/5.4/Barycentric_coordinates_2/classCGAL_1_1Barycentric__coordinates_1_1Harmonic__coordinates__2.html) to compute approximate harmonic coordinates in 2D. These coordinates satisfy all properties of barycentric coordinates inside any simple polygon.
- Added a new concept [`DiscretizedDomain_2`](https://doc.cgal.org/5.4/Barycentric_coordinates_2/classCGAL_1_1Barycentric__coordinates_1_1DiscretizedDomain__2.html) and a model of this concept called [`Delaunay_domain_2`](https://doc.cgal.org/5.4/Barycentric_coordinates_2/classCGAL_1_1Barycentric__coordinates_1_1Delaunay__domain__2.html), which is based on the [Mesh 2](https://doc.cgal.org/5.4/Manual/packages.html#PkgMesh2) package. A model of this concept is required to use [`Harmonic_coordinates_2`](https://doc.cgal.org/5.4/Barycentric_coordinates_2/classCGAL_1_1Barycentric__coordinates_1_1Harmonic__coordinates__2.html).
- Added free functions to compute Wachspress, discrete harmonic, and mean value coordinates.
- All free functions and classes are now using ranges and property maps.
### [2D and 3D Linear Geometry Kernel](https://doc.cgal.org/5.4/Manual/packages.html#PkgKernel23)
- Fixed the `intersect_2`, `compare_y_at_x_right`, and `compare_y_at_x_left` function objects of the traits class template [`Arr_geodesic_arc_on_sphere_traits_2`](https://doc.cgal.org/5.5/Arrangement_on_surface_2/classCGAL_1_1Arr__geodesic__arc__on__sphere__traits__2.html) that handles geodesic arcs on sphere and applied a small syntactical fix to the tracing traits.
- Most operations on [`CGAL::Exact_predicates_exact_constructions_kernel`](https://doc.cgal.org/5.4/Kernel_23/classCGAL_1_1Exact__predicates__exact__constructions__kernel.html) objects are now thread-safe if [`CGAL::Exact_rational`](https://doc.cgal.org/5.4/Number_types/group__nt__cgal.html#ga0849ff44771b19582218ebdfa5614f64) is [`mpq_class`](https://doc.cgal.org/5.3/Number_types/classmpq__class.html) (from `GMPXX`), `boost::multiprecision::mpq_rational` or [`CGAL::Quotient<CGAL::MP_Float>`](https://doc.cgal.org/5.3/Number_types/classCGAL_1_1MP__Float.html). The objects are not atomic though, so the usual restrictions on avoiding race conditions apply. For users who do not use threads, this can be disabled with `CGAL_HAS_NO_THREADS`.
- Added documentation for the class [`Projection_traits_3`](https://doc.cgal.org/5.4/Kernel_23/classCGAL_1_1Projection__traits__3.html), which enables the use of 2D algorithms on the projections of 3D data onto an arbitrary plane.
- Added the function [`remove_isolated_vertices()`](https://doc.cgal.org/5.5/Mesh_3/classCGAL_1_1Mesh__complex__3__in__triangulation__3.html#ace57c4e777da457c6e33b4f6e89949ce) as a post-processing step for the tetrahedral mesh generation.
- Added `construct_centroid_2_object()` and `compute_determinant_2_object()` in [`Projection_traits_xy_3`](https://doc.cgal.org/5.4/Kernel_23/classCGAL_1_1Projection__traits__xy__3.html), [`Projection_traits_xz_3`](https://doc.cgal.org/5.4/Kernel_23/classCGAL_1_1Projection__traits__xz__3.html), and [`Projection_traits_yz_3`](https://doc.cgal.org/5.4/Kernel_23/classCGAL_1_1Projection__traits__yz__3.html) classes.
- Added the function [`CGAL::Polygon_mesh_processing::orient_triangle_soup_with_reference_triangle_soup()`](https://doc.cgal.org/5.5/Polygon_mesh_processing/group__PMP__orientation__grp.html#ga855b1c55c201b91ab04eebd2811a87fd), which enables re-orienting the faces of a triangle soup based on the orientation of the nearest face in a reference triangle soup.
- Added the function [`CGAL::Polygon_mesh_processing::compatible_orientations()`](https://doc.cgal.org/5.5/Polygon_mesh_processing/group__PMP__orientation__grp.html#ga9ac9b9434084b64f3304df636c3178a3), which enables to retrieve the (in)compatibility of orientations of faces from different connected components.
- Added the function [`CGAL::Polygon_mesh_processing::tangential_relaxation()`](https://doc.cgal.org/5.5/Polygon_mesh_processing/group__PMP__meshing__grp.html#ga136c659162e5360354db5879db7431b4), which applies an area-based tangential mesh smoothing to the vertices of a surface triangle mesh.
- Added the named parameter `visitor` to the function [`triangulate_hole()`](https://doc.cgal.org/5.5/Polygon_mesh_processing/group__PMP__hole__filling__grp.html#gad2d3c43bce0ef90a16530478196d7f42), which enables to track progress with callbacks.
- Added more functions in the [visitor of the corefinement based methods](https://doc.cgal.org/5.5/Polygon_mesh_processing/classPMPCorefinementVisitor.html) to track progress.
- Added the functor [`NonZeroCoordinateIndex_3`](https://doc.cgal.org/5.4/Kernel_23/classKernel_1_1NonZeroCoordinateIndex__3.html) to the concept [`Kernel`](https://doc.cgal.org/5.4/Kernel_23/classKernel.html) with `int operator()(Vector_3)` which returns the index of any coordinate of the vector different from zero, or `-1`.
- Introduced four variations of the Garland-Heckbert simplification algorithm based on the probabilistic approach of Trettner and Kobbelt (Fast and Robust QEF Minimization using Probabilistic Quadrics): [`GarlandHeckbert_plane_policies`](https://doc.cgal.org/5.5/Surface_mesh_simplification/classCGAL_1_1Surface__mesh__simplification_1_1GarlandHeckbert__plane__policies.html), [`GarlandHeckbert_probabilistic_plane_policies`](https://doc.cgal.org/5.5/Surface_mesh_simplification/classCGAL_1_1Surface__mesh__simplification_1_1GarlandHeckbert__probabilistic__plane__policies.html), [`GarlandHeckbert_triangle_policies`](https://doc.cgal.org/5.5/Surface_mesh_simplification/classCGAL_1_1Surface__mesh__simplification_1_1GarlandHeckbert__triangle__policies.html), and [`GarlandHeckbert_probabilistic_triangle_policies`](https://doc.cgal.org/5.5/Surface_mesh_simplification/classCGAL_1_1Surface__mesh__simplification_1_1GarlandHeckbert__probabilistic__triangle__policies.html).
- The class `GarlandHeckbert_policies` has been deprecated, `GarlandHeckbert_plane_policies` replaces it.
### [Point Set Processing](https://doc.cgal.org/5.5/Manual/packages.html#PkgPointSetProcessing3)
- Most operations on [`Epeck_d`](https://doc.cgal.org/5.4/Kernel_d/structCGAL_1_1Epeck__d.html) objects are now thread-safe, see 2D and 3D Linear Geometry Kernel for details.
- A new optional named parameter, `min_points_per_cell` has been added to [`grid_simplify_point_set()`](https://doc.cgal.org/5.5/Point_set_processing_3/group__PkgPointSetProcessing3Algorithms.html#ga7757ef9b3900e42fde26f5a0ac56e20f). By adding a minimal number of points in a cell such that a point is retained, one can also filter out low density areas and outliers: in the case of densely sampled point clouds, this yields better results than using grid simplification and then outlier removal, while being very vast. The default value is `1` to keep the previous behavior as default.
- **Breaking Change:** The traits function objects `Compare_x_at_limit_2` and `Compare_x_near_limit_2` are renamed to `Compare_x_on_boundary_2` and `Compare_x_near_boundary_2`, respectively.
- Added the member function [`write_graphviz()`](https://doc.cgal.org/5.5/Spatial_searching/classCGAL_1_1Kd__tree.html#ac2851b5cafb8d5cce0dc5fb107c8f13f) to the class `Kd_tree` that writes the tree in a stream in the [Graphviz](https://graphviz.org/) format.
- A [new hierarchy of traits concepts](https://doc.cgal.org/5.4/Arrangement_on_surface_2/group__PkgArrangementOnSurface2Concepts.html) has been introduced. It captures all the valid combinations of boundary conditions for the 4 boundary sides of the parameter space. The 4 boundaries are Bottom, Top, Left, and Right. Each boundary side can be either contracted, identified, close, open, or oblivious. Not all possible combinations are valid. If one side is identified then the other must be as well. Two adjacent sides cannot be contracted.
### [CGAL and the Boost Graph Library (BGL)](https://doc.cgal.org/5.5/Manual/packages.html#PkgBGL)
- A new geometric traits, [`Arr_geodesic_arc_on_sphere_traits_2`](https://doc.cgal.org/5.4/Arrangement_on_surface_2/classCGAL_1_1Arr__geodesic__arc__on__sphere__traits__2.html) has been introduced. It handles arcs of great circles embedded on the unit sphere.
- Added the function [`invert_selection()`](https://doc.cgal.org/5.5/BGL/structCGAL_1_1Face__filtered__graph.html#aa428541ebbdd35f9a6e9a3ffd60178df) in the class [`Face_filtered_graph`](https://doc.cgal.org/5.5/BGL/structCGAL_1_1Face__filtered__graph.html), which toggles the selected status of a graph: selected faces are deselected, and unselected faces are selected.
- Added an extra parameter (`UsePolylines`) to all free functions ( [`complement()`](https://doc.cgal.org/5.4/Boolean_set_operations_2/group__boolean__complement.html), [`do_intersect()`](https://doc.cgal.org/5.4/Boolean_set_operations_2/group__boolean__do__intersect.html), [`intersection()`](https://doc.cgal.org/5.4/Boolean_set_operations_2/group__boolean__intersection.html), [`join()`](https://doc.cgal.org/5.4/Boolean_set_operations_2/group__boolean__join.html), [`difference()`](https://doc.cgal.org/5.4/Boolean_set_operations_2/group__boolean__difference.html), [`symmetric_difference()`](https://doc.cgal.org/5.4/Boolean_set_operations_2/group__boolean__symmetric__difference.html), and [`oriented_side`](https://doc.cgal.org/5.4/Boolean_set_operations_2/group__boolean__oriented__side.html)) to control whether to use `Arr_polyline_traits_2` as default traits. It is the new default as it provides better performances in general.
- Added support of weighted images for an improved quality of meshes generated from labeled images, along with a function [`CGAL::Mesh_3::generate_label_weights()`](https://doc.cgal.org/5.4/Mesh_3/namespaceCGAL_1_1Mesh__3.html#ae5914bf77180ff8948c08046154ee727) to generate the weights.
- Added the function [`CGAL::Polygon_mesh_processing::match_faces()`](https://doc.cgal.org/5.4/Polygon_mesh_processing/group__measure__grp.html#ga10f7cd81645bafe936ac5eb4e58e67ef), which, given two polygon meshes, identifies their common faces as well as faces present in only either of them.
- Added the functions: [`CGAL::Polygon_mesh_processing::bounded_error_Hausdorff_distance()`](https://doc.cgal.org/5.4/Polygon_mesh_processing/group__PMP__distance__grp.html#ga6d4ecea831c33ac10eec42b5021fc183) that computes an estimate of the one-sided Hausdorff distance between two triangle meshes which is bounded by a user-specified error bound; [`CGAL::Polygon_mesh_processing::bounded_error_symmetric_Hausdorff_distance()`](https://doc.cgal.org/5.4/Polygon_mesh_processing/group__PMP__distance__grp.html#ga9a7a682b5d9523135c8502e72117dffd) that computes an estimate of the symmetric Hausdorff distance bounded by a user-specified error bound; and [`CGAL::Polygon_mesh_processing::is_Hausdorff_distance_larger()`](https://doc.cgal.org/5.4/Polygon_mesh_processing/group__PMP__distance__grp.html#gab19e751107025a443e86baa9763aebf3) that returns `true` if the bounded-error Hausdorff distance between two meshes is larger than the user-specified max distance.
- Added the functions [`CGAL::Polygon_mesh_processing::squared_edge_length()`](https://doc.cgal.org/5.4/Polygon_mesh_processing/group__measure__grp.html#ga30fa03722cd7aa599f6dcb115f54fec5) and [`CGAL::Polygon_mesh_processing::squared_face_area()`](https://doc.cgal.org/5.4/Polygon_mesh_processing/group__measure__grp.html#ga6eda3738815fd678df225f79ccfc3e03), which, compared to [`CGAL::Polygon_mesh_processing::edge_length()`](https://doc.cgal.org/5.4/Polygon_mesh_processing/group__measure__grp.html#gae1674775d9fecada7f25710f425cff3a) and [`CGAL::Polygon_mesh_processing::face_area()`](https://doc.cgal.org/5.4/Polygon_mesh_processing/group__measure__grp.html#ga6a1d7a825c09490b1e6613295343482b), enable avoiding square-root operations.
- Added more functions in the [visitor of the corefinement based methods](https://doc.cgal.org/5.4/Polygon_mesh_processing/classPMPCorefinementVisitor.html) to track all vertex creations.
- Added an option to [`CGAL::Polygon_mesh_processing::self_intersections()`](https://doc.cgal.org/5.4/Polygon_mesh_processing/group__PMP__intersection__grp.html#gaf19c80ec12cbff7ebe9e69453f1d40b8) to report only a limited number of intersections (`maximum_number()`).
- **Breaking change**: Added the functor `Compute_squared_length_3` providing `operator(const Vector_3& v)`, which computes the squared length of `v`, to the [`HeatMethodTraits_3`](https://doc.cgal.org/5.4/Heat_method_3/classHeatMethodTraits__3.html) concept.
### [Point Set Processing](https://doc.cgal.org/5.4/Manual/packages.html#PkgPointSetProcessing3)
- Added support for [`libpointmatcher::GenericDescriptorOutlierFilter`](https://github.com/ethz-asl/libpointmatcher) that enables providing a map from a point to a weight associated with this point.
- Added new shapes to the Region Growing algorithm on a point set: circles in 2D, spheres in 3D, and cylinders in 3D.
### [CGAL and Solvers](https://doc.cgal.org/5.4/Manual/packages.html#PkgSolverInterface)
- Added support for the [OSQP solver](https://osqp.org/). This solver enables to efficiently compute the convex Quadratic Programming (QP) problems arising in the context of several packages.
Laurent Rineau