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polar2.py
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	#!/usr/bin/env python3

	import math
	from scipy.interpolate import interp1d
	import numpy as np

	class Polar :
	def __init__(self, filename) :
	f = open(filename, 'r')
	self.dict = {}
	self.angles = []
	for row in f:
	l = row.split(';')
	key = l[0]
	value = l[1:]
	self.dict[key] = value
	if key.isnumeric() :
	self.angles.append(key)
	f.close()

	def _getI(self, tws) :
	i = 0
	prev_speed = 0
	for speed in self.dict['TWA\\TWS'] :
	if tws < float(speed) :
	return i-1
	prev_speed = speed
	i += 1
	return -1

	def _getAngles(self, twa) :
	twa = int(twa/5) * 5 # reduce twa to a 5-multiple
	if twa > 180 :
	twa = twa - 2*(twa - 180)
	prev_angle = 0
	for a in self.angles :
	if twa <= float(a) :
	a = str(a)
	prev_angle = str(prev_angle)
	return prev_angle,a,self.dict[prev_angle],self.dict[a]
	prev_angle = a
	print ('*** ERROR angle {0} not found'.format(twa))
	exit(1)

	def boatSpeed(self, twa, tws) :
	i = self._getI(tws)

	twa = math.fabs(twa)
	twa = int(twa)
	if twa > 180 :
	twa = twa - 2*(twa - 180)

	a1,a2,inf,sup = self._getAngles(twa)

	x = np.array([float(a1),float(a2)])
	y = np.array([float(inf[i]), float(sup[i])])
	f = interp1d(x, y)
	try :
	speed = f(twa)
	except :
	speed = 0
	speed = float(speed)
	return speed

	#--------------------
	# Code for testing classes
	#--------------------

	if __name__ == '__main__':

	#p = Polar('../polar/figaro2.pol')
	#print ('Boat speed : {0}'.format(p.boatSpeed(45.2, 20.2)))

	p = Polar('../polar/so36i.pol')
	twa = 150
	tws = 19
	print ('boatSpeed({0},{1})'.format(twa,tws))
	print ('Boat speed : {0:.2f}'.format(p.boatSpeed(twa, tws)))