Hi Graeme,
Ouch... this is an unfortunate mixup. I derived the C++ code from cgkit
many years ago without checking. I'm changing it now to be compatible with
http://en.wikipedia.org/wiki/Rodrigues%27_rotation_formula
and the Python code in scitbx.matrix.
cctbx rev. 14644, labelit rev. 1923.
Thanks a lot for pointing out the inconsistency.
Ralf
On Thu, Jan 12, 2012 at 4:03 AM,
Hi Folks,
Just started moving code from Python to C++ - and seeing a 40x speedup which is nice - however I noticed something odd.
scitbx.matrix.col.rotate(axis, angle)
has the reversed attitude to
scitbx::vec3<double>.rotate(scitbx::vec3<double>, double angle)
viz:
this python code
s = (self._ub * hkl).rotate(self._axis, angle) q = (s + self._s0).normalize()
# check if diffracted ray parallel to detector face
q_dot_n = q.dot(detector_normal)
if q_dot_n == 0: continue
r = (q * distance / q_dot_n) - self._detector_origin
x = r.dot(self._detector_fast) y = r.dot(self._detector_slow)
if x < self._limits[0] or y < self._limits[2]: continue if x > self._limits[1] or y > self._limits[3]: continue
observed_reflection_positions.append((hkl, x, y, angle))
gives the same result as
scitbx::vec3<double> s, q, r; double x, y, q_dot_n;
/* this is rather weird - the attitude of rotation is back to front in the c++ code */
s = (ub * hkl).rotate(axis, - angle); q = (s + s0).normalize(); q_dot_n = q * normal;
if (q_dot_n == 0) return false;
r = (q * distance / q_dot_n) - origin;
x = r * fast; y = r * slow;
if (x < limits[0]) return false; if (y < limits[2]) return false; if (x > limits[1]) return false; if (y > limits[3]) return false;
prediction[0] = x; prediction[1] = y;
where I had to use -angle. Code is linked into same routines - used identically. With -angle I get numerically identical results (which is nice)
Anyone got any clues on this one?
Thanks,
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