polar2.py
b2e950483598master

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)))