code: def line2d(p0, p1):
      """
      Return 2D equation of line in the form ax+by+c = 0
      """
      # x + x1  = 0
      x0, y0 = p0[:2]
      x1, y1 = p1[:2]
      #
      if x0 == x1:
          a = -1
          b = 0
          c = x1
      elif y0 == y1:
          a = 0
          b = 1
          c = -y1
      else:
          a = y0 - y1
          b = x0 - x1
          c = x0 * y1 - x1 * y0
      return a, b, c
  
imports: from __future__ import absolute_import, division, print_function, unicode_literals
  import six
  from six.moves import zip
  import numpy
  import numpy.linalg
label_desc: Use image node_id 1 for calling a global function with example usage: line2d(p0, p1) and returns: a,  b,  c