The point-in-cell query is particularly useful with high-order meshes. It takes a 2D quad or 3D hex mesh and locates a query point in that mesh, reporting both the cell containing the point and the isoparametric coordinates of the query point within the cell.
Note
If a query point lies on the boundary in more than one cell, the point-in-cell query will return the cell with the lowest index.
If the point lies outside of any cell, the query returns the special value quest::PointInCellTraits<mesh_tag>::NO_CELL or using the MeshTraits typedef, MeshTraits::NO_CELL.
The point-in-cell query is currently implemented using MFEM, so to use this query Axom must be compiled with MFEM as a dependency. The following example (from <axom>/src/tests/quest_point_in_cell_mfem.cpp) shows the use of the query, beginning with inclusion of required header files.
../../tests/quest_point_in_cell_mfem.cpp
We use typedefs for the sake of brevity. The class is templated on a struct (provided by Quest, referred to as mesh_tag) that is used to select MFEM as the backend implementation for point location. To implement a new backend, a developer must declare a new (empty) struct and provide a specialization of the PointInCellTraits and PointInCellMeshWrapper templated on the new struct that fulfill the interface documented for those classes.
../../tests/quest_point_in_cell_mfem.cpp
Instantiate the object using an MFEM mesh and a spatial index 25 bins on a side.
../../tests/quest_point_in_cell_mfem.cpp
Test a query point. Here idx receives the ID of the cell that contains queryPoint and isoPar is a primal::Point that receives the isoparametric coordinates of queryPoint within cell idx.
../../tests/quest_point_in_cell_mfem.cpp
From cell ID and isoparametric coordinates, reconstruct the input physical coordinates.
../../tests/quest_point_in_cell_mfem.cpp
The destructor of the index object cleans up resources used (in this case, when the variable spatialIndex goes out of scope).