OpenFOAM guide/Interpolation (by cell)

This article is about the interpolation class in OpenFOAM's libfiniteVolume. For other uses, see Interpolation (disambiguation).

This article refers to classes in the interpolation (by cell) family, which includes:

• interpolation (abstract base class);
• interpolationCell;
• interpolationCellPoint; and
• interpolationCellPointFace.

These classes all perform linear interpolation on a volume field, given a cell and arbitrary location within that cell. Used by meshToMeshInterpolation. They are primarily employed by post-processing sampling utilities, such as sample.

1 interpolation (base class)

This class holds a reference to a volume field, and explicitly holds references to some of its components. It is an abstract base class that provides an interface for the other classes in this family.

2 interpolationCell

This class is an implementation of a nearest-cell interpolation, and although it appears trivial (i.e. interpolating to the nearest cell in a class that requires the cell index as a parameter!), when loaded by runTime selection by a post-processing utility, this class basically turns off interpolation. There are no explicit manifestations of this class in OpenFOAM - it is loaded exclusively by runTime selection.

3 interpolationCellPoint

Interpolate to an arbitrary location within a cell. This class works by:

• breaking each face down into triangles;
• defining tetrahedra using these triangles and the cell centre-point;
• cycling through all tetrahedra to find which encloses the arbitrary point; and
• using inverse distance weights to perform linear interpolation.

4 interpolationCellPointFace

Given an arbitrary point within the cell, find the nearest point on one of its faces. This class works by:

• finding a candidate face by projecting a line from the cell-centre through the arbitrary point;
• decomposing the cell face into traingles that include the face centre-point and two vertices;
• defining tetrahedra using these triangles and the cell centre-point;
• searches for the tetrahedron enclosing the point;
• if this fails, it repeats this for all faces;
• if the face is not an empty fvpatch, it returns the normal projection of the point onto the selected face;
• if the face is an empty fvpatch, it returns the cell centre instead.