Tolerances

Support for uniform tolerances. More...

Collaboration diagram for Tolerances:

Files
file	tol.h

Data Structures
struct	bn_tol

Macros
#define	BN_CK_TOL(_p)   BU_CKMAG(_p, BN_TOL_MAGIC, "bn_tol")
#define	BN_TOL_INIT(_p)
#define	BN_TOL_INIT_ZERO   { BN_TOL_MAGIC, 0.0, 0.0, 0.0, 1.0 }
#define	BN_TOL_IS_INITIALIZED(_p)   (((struct bn_tol *)(_p) != (struct bn_tol *)0) && LIKELY((_p)->magic == BN_TOL_MAGIC))
#define	BN_TOL_DIST   0.0005
#define	BN_VECT_ARE_PARALLEL(_dot, _tol)    (((_dot) <= -SMALL_FASTF) ? (NEAR_EQUAL((_dot), -1.0, (_tol)->perp)) : (NEAR_EQUAL((_dot), 1.0, (_tol)->perp)))
#define	BN_VECT_ARE_PERP(_dot, _tol)    (((_dot) < 0) ? ((-(_dot))<=(_tol)->perp) : ((_dot) <= (_tol)->perp))

Detailed Description

Support for uniform tolerances.

A handy way of passing around the tolerance information needed to perform approximate floating-point calculations on geometry.

dist & dist_sq establish the distance tolerance.

If two points are closer together than dist, then they are to be considered the same point.

For example:

point_t a, b;
vect_t diff;
VSUB2(diff, a, b);
if (MAGNITUDE(diff) < tol->dist)        a & b are the same.
or, more efficiently:
if (MAQSQ(diff) < tol->dist_sq)

perp & para establish the angular tolerance.

If two rays emanate from the same point, and their dot product is nearly one, then the two rays are the same, while if their dot product is nearly zero, then they are perpendicular.

For example:

vect_t a, b;
if (fabs(VDOT(a, b)) >= tol->para)      a & b are parallel
if (fabs(VDOT(a, b)) <= tol->perp)      a & b are perpendicular

Note

tol->dist_sq = tol->dist * tol->dist;
tol->para = 1 - tol->perp;

Macro Definition Documentation

BN_CK_TOL

#define BN_CK_TOL

(

_p

)

BU_CKMAG(_p, BN_TOL_MAGIC, "bn_tol")

asserts the validity of a bn_tol struct.

Definition at line 83 of file tol.h.

BN_TOL_INIT

#define BN_TOL_INIT

(

_p

)

Value:

        { \
        (_p)->magic = BN_TOL_MAGIC; \
        (_p)->dist = 0.0; \
        (_p)->dist_sq = 0.0; \
        (_p)->perp = 0.0; \
        (_p)->para = 1.0; \
    }

initializes a bn_tol struct to zero without allocating any memory.

Definition at line 88 of file tol.h.

BN_TOL_INIT_ZERO

#define BN_TOL_INIT_ZERO   { BN_TOL_MAGIC, 0.0, 0.0, 0.0, 1.0 }

macro suitable for declaration statement zero-initialization of a bn_tol struct.

Definition at line 100 of file tol.h.

BN_TOL_IS_INITIALIZED

#define BN_TOL_IS_INITIALIZED

(

_p

)

(((struct bn_tol *)(_p) != (struct bn_tol *)0) && LIKELY((_p)->magic == BN_TOL_MAGIC))

returns truthfully whether a bn_tol struct has been initialized.

Definition at line 105 of file tol.h.

BN_TOL_DIST

#define BN_TOL_DIST   0.0005

replaces the hard coded tolerance value

Definition at line 110 of file tol.h.

BN_VECT_ARE_PARALLEL

#define BN_VECT_ARE_PARALLEL	(		_dot,
			_tol
	)		(((_dot) <= -SMALL_FASTF) ? (NEAR_EQUAL((_dot), -1.0, (_tol)->perp)) : (NEAR_EQUAL((_dot), 1.0, (_tol)->perp)))

returns truthfully whether a given dot-product of two unspecified vectors are within a specified parallel tolerance.

Definition at line 116 of file tol.h.

BN_VECT_ARE_PERP

#define BN_VECT_ARE_PERP	(		_dot,
			_tol
	)		(((_dot) < 0) ? ((-(_dot))<=(_tol)->perp) : ((_dot) <= (_tol)->perp))

returns truthfully whether a given dot-product of two unspecified vectors are within a specified perpendicularity tolerance.

Definition at line 123 of file tol.h.