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## CGAL::Alpha_status<NT>

### Definition

The class Alpha_status<NT> is a small data strructure to store the critical alpha values of faces of an alpha shape. Each face has three critical alpha values, called alpha_min, alpha_mid and alpha_max in increasing order. The face will be exterior for any < alpha_min, singular for alpha_min < alpha_mid, regular for alpha_mid < alpha_max and interior for alpha_max alpha. The value alpha_min is undefined for faces which are not Gabriel faces and therefore do not appear in the alpha complex without any of their including face. The value alpha_max is undefined for convex hull faces which can never be interior, The data structure also includes two boolean to mark if the face is a Gabriel face or a convex hull face.

The class Alpha_status<NT> is paremetrized by a number type NT.

#include <CGAL/Alpha_shape_cell_base_3.h>

### Creation

Alpha_status<NT> a;
| default constructor.

### Modifiers

void | a.set_is_Gabriel ( bool yesorno)
|  | sets Gabriel marker;
void | a.set_is_on_chull ( bool yesorno)
|  | sets convex hull marker;
void | a.set_alpha_min ( NT alpha)
|  | sets alpha_min.
void | a.set_alpha_mid ( NT alpha)
|  | sets alpha_mid.
void | a.set_alpha_max ( NT alpha)
|  | sets alpha_max.

### Access Functions

bool | a.is_Gabriel () | Returns true for Gabriel faces;
bool | a.is_on_chull () | Returns true forconvex hull faces;
NT | a.alpha_min () | Returns the alpha_min Precondition: is_Gabriel() returns false;
NT | a.alpha_mid () | Returns the alpha_mid;
NT | a.alpha_max () | Returns alpha_max. Precondition: is_on_chull() returns false.

### See Also

AlphaShapeCellBase_3
AlphaShapeVertexBase_3

Next: WeightedAlphaShapeTraits_3

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The CGAL Project . Tue, December 21, 2004 .