Grid orientations
[Combinatoric Algorithms on Grids]

Algorithms related to orientation of grids. More...

Collaboration diagram for Grid orientations:

Functions
template<class G , class GT >
bool	GrAL::get_orientation (G const &g, GT &orientation)
	Determine relative orientation of cells.
template<class G , class C >
bool	GrAL::fix_orientation (G &g, C guide_cell)
	Change orientation of cells such that it is consistent.
template<class G >
bool	GrAL::fix_orientation (G &g)
	Convenience wrapper for orientation.

---

Detailed Description

Algorithms related to orientation of grids.

---

Function Documentation

template<class G , class GT >

bool GrAL::get_orientation	(	G const &	g,
		GT &	orientation
	)			[inline]

Determine relative orientation of cells.

Template parameters:

• G
  • Model of CellRange
  • type FacetOnCellIterator
  • The function int relative_orientation(FacetOnCellIterator f1, FacetOnCellIterator f2) has been overloaded for G::FacetOnCellIterator and returns the relative orientation of the facet *f1 == *f2 induced by f1 and f2. For instance, in a 2D grid, this means that if the edge *f1 is represented with opposite vertex ordering by f1 and f2, the result should be -1, and +1 otherwise.
• GF
  • Model of cell based MutableGridFunction

Parameters:

	g	input grid
	orientation	output grid function indicating orientation changes

Returns:

true if the grid is orientable, and false otherwise.

Precondition:

g is a manifold-with-boundary grid

orientation is bound to g

Postcondition:

On return, orientation(c) is positive if the orientation does not need to be changed, and negative otherwise. The absolute value of orientation(c) indicates the connected component of c.

Note:

The orientation flags in orientation are computed on a purely combinatorial basis. If an orientation with a geometric meaning is wanted (e.g. producing outward pointing normals in the case of a manifold grid embedded in an dim(g)+1 dimensional space, one has to flip, orientations of either all cells with positive or all cells with negative flags, for each component independently.

See also:

Tested in test-orientation.C

Definition at line 76 of file orientation.h.

References relative_orientation().

Referenced by GrAL::fix_orientation().

template<class G , class C >

bool GrAL::fix_orientation	(	G &	g,
		C	guide_cell
	)			[inline]

Change orientation of cells such that it is consistent.

Template parameters:

• G
  • Model of CellRange
  • type FacetOnCellIterator
  • function swap_orientation(Cell)
  • The function int relative_orientation(FacetOnCellIterator f1, FacetOnCellIterator f2) has been overloaded for G::FacetOnCellIterator and returns the relative orientation of the facet *f1 == *f2 induced by f1 and f2. For instance, in a 2D grid, this means that if the edge *f1 is represented with opposite vertex ordering by f1 and f2, the result should be -1, and +1 otherwise.

C

• Model of GridCell

  Parameters:

  	g	input grid, orientation of some cells will be changed on output
  	\c	guide_cell Cell with reference orientation

  Returns:

  true if the grid is orientable, and false otherwise.

  Precondition:

  g is a manifold-with-boundary grid

  c g

  Postcondition:

  On return, g is oriented consistent with guide_cell, such that a call to get_orientation(g, orient) will yield orientation(c) == 1 for each cell c of g.

  See also:

  Tested in test-orientation.C

  Todo:

  Extend to list of guide cells for disconnected grids.

Definition at line 154 of file orientation.h.

References GrAL::get_orientation().

Referenced by GrAL::fix_orientation().

template<class G >

bool GrAL::fix_orientation

(

G &

g

)

[inline]

Convenience wrapper for orientation.

Equivalent to fix_orientation(g, * g.FirstCell())

Definition at line 173 of file orientation.h.

References GrAL::fix_orientation().