mavextra.py

#!/usr/bin/env python
'''
useful extra functions for use by mavlink clients

Copyright Andrew Tridgell 2011
Released under GNU GPL version 3 or later
'''

from math import *


def kmh(mps):
    '''convert m/s to Km/h'''
    return mps*3.6

def altitude(press_abs, ground_press=955.0, ground_temp=30):
    '''calculate barometric altitude'''
    return log(ground_press/press_abs)*(ground_temp+273.15)*29271.267*0.001


def mag_heading(RAW_IMU, ATTITUDE, declination=0, SENSOR_OFFSETS=None, ofs=None):
    '''calculate heading from raw magnetometer'''
    mag_x = RAW_IMU.xmag
    mag_y = RAW_IMU.ymag
    mag_z = RAW_IMU.zmag
    if SENSOR_OFFSETS is not None and ofs is not None:
        mag_x += ofs[0] - SENSOR_OFFSETS.mag_ofs_x
        mag_y += ofs[1] - SENSOR_OFFSETS.mag_ofs_y
        mag_z += ofs[2] - SENSOR_OFFSETS.mag_ofs_z

    headX = mag_x*cos(ATTITUDE.pitch) + mag_y*sin(ATTITUDE.roll)*sin(ATTITUDE.pitch) + mag_z*cos(ATTITUDE.roll)*sin(ATTITUDE.pitch)
    headY = mag_y*cos(ATTITUDE.roll) - mag_z*sin(ATTITUDE.roll)
    heading = degrees(atan2(-headY,headX)) + declination
    if heading < 0:
        heading += 360
    return heading

def mag_field(RAW_IMU, SENSOR_OFFSETS=None, ofs=None):
    '''calculate magnetic field strength from raw magnetometer'''
    mag_x = RAW_IMU.xmag
    mag_y = RAW_IMU.ymag
    mag_z = RAW_IMU.zmag
    if SENSOR_OFFSETS is not None and ofs is not None:
        mag_x += ofs[0] - SENSOR_OFFSETS.mag_ofs_x
        mag_y += ofs[1] - SENSOR_OFFSETS.mag_ofs_y
        mag_z += ofs[2] - SENSOR_OFFSETS.mag_ofs_z
    return sqrt(mag_x**2 + mag_y**2 + mag_z**2)

def angle_diff(angle1, angle2):
    '''show the difference between two angles in degrees'''
    ret = angle1 - angle2
    if ret > 180:
        ret -= 360;
    if ret < -180:
        ret += 360
    return ret


lowpass_data = {}

def lowpass(var, key, factor):
    '''a simple lowpass filter'''
    global lowpass_data
    if not key in lowpass_data:
        lowpass_data[key] = var
    else:
        lowpass_data[key] = factor*lowpass_data[key] + (1.0 - factor)*var
    return lowpass_data[key]

last_delta = {}

def delta(var, key):
    '''calculate slope'''
    global last_delta
    dv = 0
    if key in last_delta:
        dv = var - last_delta[key]
    last_delta[key] = var
    return dv

def delta_angle(var, key):
    '''calculate slope of an angle'''
    global last_delta
    dv = 0
    if key in last_delta:
        dv = var - last_delta[key]
    last_delta[key] = var
    if dv > 180:
        dv -= 360
    if dv < -180:
        dv += 360
    return dv

def roll_estimate(RAW_IMU,smooth=0.7):
    '''estimate roll from accelerometer'''
    rx = lowpass(RAW_IMU.xacc,'rx',smooth)
    ry = lowpass(RAW_IMU.yacc,'ry',smooth)
    rz = lowpass(RAW_IMU.zacc,'rz',smooth)
    return degrees(-asin(ry/sqrt(rx**2+ry**2+rz**2)))

def pitch_estimate(RAW_IMU, smooth=0.7):
    '''estimate pitch from accelerometer'''
    rx = lowpass(RAW_IMU.xacc,'rx',smooth)
    ry = lowpass(RAW_IMU.yacc,'ry',smooth)
    rz = lowpass(RAW_IMU.zacc,'rz',smooth)
    return degrees(asin(rx/sqrt(rx**2+ry**2+rz**2)))

def gravity(RAW_IMU, SENSOR_OFFSETS=None, ofs=None, smooth=0.7):
    '''estimate pitch from accelerometer'''
    rx = RAW_IMU.xacc
    ry = RAW_IMU.yacc
    rz = RAW_IMU.zacc+45
    if SENSOR_OFFSETS is not None and ofs is not None:
        rx += ofs[0] - SENSOR_OFFSETS.accel_cal_x
        ry += ofs[1] - SENSOR_OFFSETS.accel_cal_y
        rz += ofs[2] - SENSOR_OFFSETS.accel_cal_z
    return lowpass(sqrt(rx**2+ry**2+rz**2)*0.01,'_gravity',smooth)



def pitch_sim(SIMSTATE, GPS_RAW):
    '''estimate pitch from SIMSTATE accels'''
    xacc = SIMSTATE.xacc - lowpass(delta(GPS_RAW.v,"v")*6.6, "v", 0.9)
    zacc = SIMSTATE.zacc
    zacc += SIMSTATE.ygyro * GPS_RAW.v;
    if xacc/zacc >= 1:
        return 0
    if xacc/zacc <= -1:
        return -0
    return degrees(-asin(xacc/zacc))

def distance_two(GPS_RAW1, GPS_RAW2):
    '''distance between two points'''
    lat1 = radians(GPS_RAW1.lat)
    lat2 = radians(GPS_RAW2.lat)
    lon1 = radians(GPS_RAW1.lon)
    lon2 = radians(GPS_RAW2.lon)
    dLat = lat2 - lat1
    dLon = lon2 - lon1

    a = sin(0.5*dLat) * sin(0.5*dLat) + sin(0.5*dLon) * sin(0.5*dLon) * cos(lat1) * cos(lat2)
    c = 2.0 * atan2(sqrt(a), sqrt(1.0-a))
    return 6371 * 1000 * c


first_fix = None

def distance_home(GPS_RAW):
    '''distance from first fix point'''
    global first_fix
    if first_fix == None or first_fix.fix_type < 2:
        first_fix = GPS_RAW
        return 0
    return distance_two(GPS_RAW, first_fix)