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## calculate angle between two points defined for lat / lon (angle = 0 degrees is North)
def angle_points(lat1,lon1,lat2,lon2,outunit='degrees'):
  """
  inputs: lat1, lon1, lat2, lon2 = degress
  outputs: degrees
  """
  from math import atan2,degrees,radians
  dlat = lat2 - lat1
  dlon = lon2 - lon1
  if outunit=='degrees': return 90. - degrees(atan2(dlat,dlon))
  else: return radians(90. - degrees(atan2(dlat,dlon)))