Description Usage Arguments Details Value Author(s) References Examples
The affine/rotation matrix R is calculated from the quaternion parameters.
1 2 | quaternion2mat44(nim, tol = 1e-7)
quaternion2rotation(b, c, d, tol = 1e-7)
|
nim |
is an object of class |
tol |
is a very small value used to judge if a number is essentially zero. |
b |
is the quaternion b parameter. |
c |
is the quaternion c parameter. |
d |
is the quaternion d parameter. |
The quaternion representation is chosen for its compactness in
representing rotations. The orientation of the (x,y,z) axes
relative to the (i,j,k) axes in 3D space is specified using a
unit quaternion [a,b,c,d], where
a*a+b*b+c*c+d*d=1. The
(b,c,d) values are all that is needed, since we require that
a=sqrt(1.0-(b*b+c*c+d*d)) be
non-negative. The (b,c,d) values are stored in the
(quatern_b
, quatern_c
, quatern_d
) fields.
The (proper) 3x3 rotation matrix or 4x4 affine matrix.
Brandon Whitcher bwhitcher@gmail.com
NIfTI-1
http://nifti.nimh.nih.gov/
1 2 3 | ## This R matrix is represented by quaternion [a,b,c,d] = [0,1,0,0]
## (which encodes a 180 degree rotation about the x-axis).
(R <- quaternion2rotation(1, 0, 0))
|
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