NAME

	qtom, mtoq, qadd, qsub, qneg, qmul, qdiv, qunit, qinv, qlen, slerp, qmid, qsqrt – Quaternion arithmetic

SYNOPSIS

#include <draw.h> #include <geometry.h> Quaternion qadd(Quaternion q, Quaternion r) Quaternion qsub(Quaternion q, Quaternion r) Quaternion qneg(Quaternion q) Quaternion qmul(Quaternion q, Quaternion r) Quaternion qdiv(Quaternion q, Quaternion r) Quaternion qinv(Quaternion q) double qlen(Quaternion p) Quaternion qunit(Quaternion q) void qtom(Matrix m, Quaternion q) Quaternion mtoq(Matrix mat) Quaternion slerp(Quaternion q, Quaternion r, double a) Quaternion qmid(Quaternion q, Quaternion r) Quaternion qsqrt(Quaternion q)

DESCRIPTION

The Quaternions are a non-commutative extension field of the Real numbers, designed to do for rotations in 3-space what the complex numbers do for rotations in 2-space. Quaternions have a real component r and an imaginary vector component v=(i,j,k). Quaternions add componentwise and multiply according to the rule (r,v)(s,w)=(rs-v.w, rw+vs+vxw), where . and x are the ordinary vector dot and cross products. The multiplicative inverse of a non-zero quaternion (r,v) is (r,-v)/(r2-v.v). The following routines do arithmetic on quaternions, represented as typedef struct Quaternion Quaternion; struct Quaternion{ double r, i, j, k; }; Name   Description qadd   Add two quaternions. qsub   Subtract two quaternions. qneg   Negate a quaternion. qmul   Multiply two quaternions. qdiv   Divide two quaternions. qinv   Return the multiplicative inverse of a quaternion. qlen   Return sqrt(q.r*q.r+q.i*q.i+q.j*q.j+q.k*q.k), the length of a quaternion. qunit   Return a unit quaternion (length=1) with components proportional to q’s. A rotation by angle θ about axis A (where A is a unit vector) can be represented by the unit quaternion q=(cos θ/2, Asin θ/2). The same rotation is represented by -q; a rotation by -θ about -A is the same as a rotation by θ about A. The quaternion q transforms points by (0,x’,y’,z’) = q-1(0,x,y,z)q. Quaternion multiplication composes rotations. The orientation of an object in 3-space can be represented by a quaternion giving its rotation relative to some ‘standard’ orientation. The following routines operate on rotations or orientations represented as unit quaternions: mtoq   Convert a rotation matrix (see matrix(3)) to a unit quaternion. qtom   Convert a unit quaternion to a rotation matrix. slerp   Spherical lerp. Interpolate between two orientations. The rotation that carries q to r is q-1r, so slerp(q, r, t) is q(q-1r)t. qmid   slerp(q, r, .5) qsqrt   The square root of q. This is just a rotation about the same axis by half the angle.

SOURCE

	/home/opt/plan9port/src/libgeometry/quaternion.c

SEE ALSO

	matrix(3), qball(3)

BUGS

	To avoid name conflicts with NetBSD, qdiv is a preprocessor macro defined as p9qdiv; see intro(3).