Quatern3dC - Quaternion

User Documentation

RAVL, Recognition And Vision Library

Ravl - Math - Geometry - 3D - Quatern3dC

Quatern3dC

Quaternion

include	"Ravl/Quatern3d.hh"
Created:	13/11/95
User Level:	Normal
Library:	RavlMath
In Scope:	RavlN

Comments:
Two quarternions may represent the same rotation q and -q, both are valid, but it can be convenient to keep q[0]>0. This code usually tries to keep q[0] positive. All the non trivial constructors build a quarternion with q[0]>=0. The multiply operation can exit with q[0]<0, this is necessary if the Rotate member function is to work.

There are many tricky conversions, and stability issues with rotations and the conversions. Be careful of angles in particular angles near 0 or PI. This affects some conversions as indicated

A "valid" quarternion has norm 1, however when a quarternion contains a vector it does not have norm 1. Be careful when using operations that may cause the quarternion not to be valid.

When a quarternion is read in it should always be normalised so that it obeys normalisation to full machine precision which is the normal state of affairs

In addition it is possible that small errors may creep in during repeated multiplication. The user should consider using the Normalize() function to correct this. It is NOT done automatically during multiplication.

Variables:

Methods:

Constructors

Quatern3dC(): Null Constructor, zero rotation, (1,0,0,0)
Quatern3dC(RealT q0,RealT q1,RealT q2,RealT q3): Constructor - quarternion is not tested for validity.
Quatern3dC(const Vector3dC & axtheta): Constructor from axis * angle in radians
Quatern3dC(const Vector3dC & axis,RealT theta): Constructor
If theta != zero then axis must be non zero the axis vector is normalized inside this routine!
Quatern3dC(const Matrix3dC & rotate,bool check = true): Constructor
matrix is checked for orthogonality if check!=0 This routine is reliable for small angles!! NOT ACCURATE FOR ANGLES NEAR PI

General operations

void Set(const Vector3dC & axtheta): Set as specifed
void Set(const Vector3dC & axis,RealT theta): Set as specifed
void Set(const Matrix3dC & rotate,bool check = true): Set as specifed
RealT & operator [](UIntT i): Access to ith element of the quarternion
RealT operator [](UIntT i) const: Access to ith element of the quarternion
void MakePositive(void): replace quarternion by one with q[0] positive which performs the same rotation
RealT Norm(): the norm of the quaternion (quareroot of the sum of the squares of the elements)
void Normalize(void): impose the condition that norm=1
Quatern3dC Inverse() const: returns inverse of q, does not change q (Doesn't normalize q; is in fact the conjugate of q)
Quatern3dC Conjugate() const: Conjugate
Quatern3dC I() const: returns inverse of q, does not change q
Vector3dC Rotate(Vector3dC r) const: applies rotation q to r and returns the result
Vector3dC ExportAxTheta() const: return the rotation as a unit vector axis times angle in radians Note warnings for ExportRotAxis();
RealT ExportRotationAngle() const: return the angle of rotation, which should always be 0-PI I believe this routine is accurate for theta near 0 and near PI
Vector3dC ExportRotationAxis() const: return the rotation as a unit vector axis around which rotated If Null Rotation return axis as (1,1,1) vector ********** NB ************ For angles very close to PI this routines is not reliable but it is OK for angles near zero. If angle==PI the axis is garbage!
Matrix4dC ExportQuatMat() const: return quaternion as a 4x4 matrix - see Schmitts ECCV 98 paper
MatrixC ExportQuatMat2() const: return quaternion as a MatrixC (4x4) - see Schmitts ECCV 98 paper
Matrix3dC ExportRotationMatrix(bool normalize = false) const: return rotation as 3x3 rotation matrix as far as I know always OK
Vector3dC ExportVector() const: returns the 3 vector components as they are, used for rotating vectors
Vector3dC ExportEuler() const: The angles returned correspond to rotations around static axes XYZ in radians.
Vector3dC ExportEuler(const JointT & jtype,const bool & premult) const: The angles returned correspond to rotations
MatrixC DQuatDRotVec() const: derivative of the quaternion to the rotation vector
MatrixC DRotVecDQuat() const: derivative of the rotation vector to the quaternion
RealT func_alpha(const RealT & x,const RealT & thres) const
RealT func_gRavl(const RealT & x,const RealT & thres) const
RealT func_kappa(const RealT & x,const RealT & thres) const
RealT func_lambda(const RealT & x,const RealT & thres) const
RealT func_tau(const RealT & thres) const
RealT func_ups(const RealT & thres) const: functions used in DQuatDRotVec & DRotVecDQuat
MatrixC Dq0q1Dq(const Quatern3dC & q,const int & nr) const: derivative of the product ('this' * 'q') with respect to 'this' (nr=0)
or 'q' (nr=1)
MatrixC Dq0q1q2Dq(const Quatern3dC & q1,const Quatern3dC & q2,const int & nr) const: derivative of the product ('this' * 'q1' * 'q2') with respect to
'this' (nr=0), 'q1' (nr=1) or 'q2' (nr=2)
void Print() const: short print out
void LongPrint() const: detailed print out
Quatern3dC operator *(const Quatern3dC p) const: returns q x p, quarternion multiplication can return q[0] < 0
Quatern3dC operator *(const RealT & val) const: returns q[i] = q1[i]*val, for i=0..3
Quatern3dC operator +(const Quatern3dC & p) const: returns q[i] = q1[i] + q2[i], for i=0..3
Quatern3dC operator -(const Quatern3dC & p) const: returns q[i] = q1[i] - q2[i], for i=0..3
ostream & operator <<(ostream & outS,const Quatern3dC & quartern): ouput stream operator

Maintainer:Andrew Stoddart, Created: 13/11/95, Documentation by CxxDoc: Tue Aug 13 09:59:02 2002