Convert RSSI to distance to AP.

rssi.py

#! /usr/bin/env python3

from matplotlib import pyplot as plt
import math

# hyper parameters
calib1m_rssi = -43  #!< bias of rssi in 1 meter
propa = 2.8         
scale_factor = 10  #!< scale factor of distance input of level function

# measured_rssi -> distance(meter)
dist = lambda value : math.pow(10,((calib1m_rssi-value)/(10.0*propa)))

# measured_rssi -> displayed signal level [0-9]
level = lambda value : int(9*math.exp(-dist(value)/scale_factor))

# testing 

# samples for testing
measured_rssi = range(-100,1,1)

dists  = map(dist,measured_rssi)
levels = map(level,measured_rssi)

plt.plot(list(measured_rssi),list(dists))
plt.scatter(list(measured_rssi),list(levels))
plt.show()

#for d,l in zip(dists,levels):
#    print(d,l)