code: def arcball_constrain_to_axis(point, axis):
      """Return sphere point perpendicular to axis."""
      v = numpy.array(point, dtype=numpy.float64, copy=True)
      a = numpy.array(axis, dtype=numpy.float64, copy=True)
      v -= a * numpy.dot(a, v)  # on plane
      n = vector_norm(v)
      if n > _EPS:
          if v[2] < 0.0:
              numpy.negative(v, v)
          v /= n
          return v
      if a[2] == 1.0:
          return numpy.array([1.0, 0.0, 0.0])
      return unit_vector([-a[1], a[0], 0.0])
  
imports: import math
  import numpy
label_desc: Use image node_id 36 for calling a global function with example usage: arcball_constrain_to_axis(point, axis) and returns: unit_vector, v, numpy