[cctbxbb] Attitude of rotation, Python to C++

Graeme.Winter at Diamond.ac.uk Graeme.Winter at Diamond.ac.uk
Thu Jan 12 04:03:56 PST 2012

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)


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:
            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]:
            if x > self._limits[1] or y > self._limits[3]:

            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?


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