Simple Python HTTP server that provides an API to turn Fitbit watch orientation data into commands to a pan-tilt unit

server.py

import SocketServer
import SimpleHTTPServer
import math
import json
import pantilthat

pantilthat.pan(0)
pantilthat.tilt(0)

PORT = 9090

# From https://computergraphics.stackexchange.com/questions/8195/how-to-convert-euler-angles-to-quaternions-and-get-the-same-euler-angles-back-fr
def quaternion_to_euler(x, y, z, w):
    t0 = +2.0 * (w * x + y * z)
    t1 = +1.0 - 2.0 * (x * x + y * y)
    roll = math.atan2(t0, t1)
    t2 = +2.0 * (w * y - z * x)
    t2 = +1.0 if t2 > +1.0 else t2
    t2 = -1.0 if t2 < -1.0 else t2
    pitch = math.asin(t2)
    t3 = +2.0 * (w * z + x * y)
    t4 = +1.0 - 2.0 * (y * y + z * z)
    yaw = math.atan2(t3, t4)
    return [yaw, pitch, roll]

class CustomHandler(SimpleHTTPServer.SimpleHTTPRequestHandler):
    def do_POST(self):
        content_length = int(self.headers['Content-Length'])
        body = self.rfile.read(content_length)
        #print (body)
        x = json.loads(body)
        if x.has_key("orientation"):
            euler = quaternion_to_euler(
                float(x["orientation"][1]),
                float(x["orientation"][2]),
                float(x["orientation"][3]),
                float(x["orientation"][0]))
            # Bring in to range 0-2*Pi to avoid a discontinuity in the middle
            if euler[2] < 0:
                euler[2] = euler[2] + math.pi * 2.0;
            tilt = math.degrees(euler[2]) - 180
            tilt = max(tilt, -30) # Limit to +/- 30 degrees
            tilt = min(tilt, 30)
            pantilthat.tilt(tilt)
            pan = math.degrees(euler[1])
            pan = max(pan, -30) # Limit to +/- 30 degrees
            pan = min(pan, 30)
            pantilthat.pan(pan)
            print(pan,tilt)
        self.send_response(200)
        self.send_header('Content-type','text/txt')
        self.end_headers()
        self.wfile.write("OK")

httpd = SocketServer.ThreadingTCPServer(('', PORT),CustomHandler)

print "serving at port", PORT
httpd.serve_forever()