#!/usr/bin/env python
# parse and construct FlightGear NET FDM packets
# Andrew Tridgell, November 2011
# released under GNU GPL version 2 or later
import struct, math
class fgFDMError(Exception):
'''fgFDM error class'''
def __init__(self, msg):
Exception.__init__(self, msg)
self.message = 'fgFDMError: ' + msg
class fgFDMVariable(object):
'''represent a single fgFDM variable'''
def __init__(self, index, arraylength, units):
self.index = index
self.arraylength = arraylength
self.units = units
class fgFDMVariableList(object):
'''represent a list of fgFDM variable'''
def __init__(self):
self.vars = {}
self._nextidx = 0
def add(self, varname, arraylength=1, units=None):
self.vars[varname] = fgFDMVariable(self._nextidx, arraylength, units=units)
self._nextidx += arraylength
class fgFDM(object):
'''a flightgear native FDM parser/generator'''
def __init__(self):
'''init a fgFDM object'''
self.FG_NET_FDM_VERSION = 24
self.pack_string = '>I 4x 3d 6f 11f 3f 2f I 4I 4f 4f 4f 4f 4f 4f 4f 4f 4f I 4f I 3I 3f 3f 3f I i f 10f'
self.values = [0]*98
self.FG_MAX_ENGINES = 4
self.FG_MAX_WHEELS = 3
self.FG_MAX_TANKS = 4
# supported unit mappings
self.unitmap = {
('radians', 'degrees') : math.degrees(1),
('rps', 'dps') : math.degrees(1),
('feet', 'meters') : 0.3048,
('fps', 'mps') : 0.3048,
('knots', 'mps') : 0.514444444,
('knots', 'fps') : 0.514444444/0.3048,
('fpss', 'mpss') : 0.3048,
('seconds', 'minutes') : 60,
('seconds', 'hours') : 3600,
}
# build a mapping between variable name and index in the values array
# note that the order of this initialisation is critical - it must
# match the wire structure
self.mapping = fgFDMVariableList()
self.mapping.add('version')
# position
self.mapping.add('longitude', units='radians') # geodetic (radians)
self.mapping.add('latitude', units='radians') # geodetic (radians)
self.mapping.add('altitude', units='meters') # above sea level (meters)
self.mapping.add('agl', units='meters') # above ground level (meters)
# attitude
self.mapping.add('phi', units='radians') # roll (radians)
self.mapping.add('theta', units='radians') # pitch (radians)
self.mapping.add('psi', units='radians') # yaw or true heading (radians)
self.mapping.add('alpha', units='radians') # angle of attack (radians)
self.mapping.add('beta', units='radians') # side slip angle (radians)
# Velocities
self.mapping.add('phidot', units='rps') # roll rate (radians/sec)
self.mapping.add('thetadot', units='rps') # pitch rate (radians/sec)
self.mapping.add('psidot', units='rps') # yaw rate (radians/sec)
self.mapping.add('vcas', units='fps') # calibrated airspeed
self.mapping.add('climb_rate', units='fps') # feet per second
self.mapping.add('v_north', units='fps') # north velocity in local/body frame, fps
self.mapping.add('v_east', units='fps') # east velocity in local/body frame, fps
self.mapping.add('v_down', units='fps') # down/vertical velocity in local/body frame, fps
self.mapping.add('v_wind_body_north', units='fps') # north velocity in local/body frame
self.mapping.add('v_wind_body_east', units='fps') # east velocity in local/body frame
self.mapping.add('v_wind_body_down', units='fps') # down/vertical velocity in local/body
# Accelerations
self.mapping.add('A_X_pilot', units='fpss') # X accel in body frame ft/sec^2
self.mapping.add('A_Y_pilot', units='fpss') # Y accel in body frame ft/sec^2
self.mapping.add('A_Z_pilot', units='fpss') # Z accel in body frame ft/sec^2
# Stall
self.mapping.add('stall_warning') # 0.0 - 1.0 indicating the amount of stall
self.mapping.add('slip_deg', units='degrees') # slip ball deflection
# Engine status
self.mapping.add('num_engines') # Number of valid engines
self.mapping.add('eng_state', self.FG_MAX_ENGINES) # Engine state (off, cranking, running)
self.mapping.add('rpm', self.FG_MAX_ENGINES) # Engine RPM rev/min
self.mapping.add('fuel_flow', self.FG_MAX_ENGINES) # Fuel flow gallons/hr
self.mapping.add('fuel_px', self.FG_MAX_ENGINES) # Fuel pressure psi
self.mapping.add('egt', self.FG_MAX_ENGINES) # Exhuast gas temp deg F
self.mapping.add('cht', self.FG_MAX_ENGINES) # Cylinder head temp deg F
self.mapping.add('mp_osi', self.FG_MAX_ENGINES) # Manifold pressure
self.mapping.add('tit', self.FG_MAX_ENGINES) # Turbine Inlet Temperature
self.mapping.add('oil_temp', self.FG_MAX_ENGINES) # Oil temp deg F
self.mapping.add('oil_px', self.FG_MAX_ENGINES) # Oil pressure psi
# Consumables
self.mapping.add('num_tanks') # Max number of fuel tanks
self.mapping.add('fuel_quantity', self.FG_MAX_TANKS)
# Gear status
self.mapping.add('num_wheels')
self.mapping.add('wow', self.FG_MAX_WHEELS)
self.mapping.add('gear_pos', self.FG_MAX_WHEELS)
self.mapping.add('gear_steer', self.FG_MAX_WHEELS)
self.mapping.add('gear_compression', self.FG_MAX_WHEELS)
# Environment
self.mapping.add('cur_time', units='seconds') # current unix time
self.mapping.add('warp', units='seconds') # offset in seconds to unix time
self.mapping.add('visibility', units='meters') # visibility in meters (for env. effects)
# Control surface positions (normalized values)
self.mapping.add('elevator')
self.mapping.add('elevator_trim_tab')
self.mapping.add('left_flap')
self.mapping.add('right_flap')
self.mapping.add('left_aileron')
self.mapping.add('right_aileron')
self.mapping.add('rudder')
self.mapping.add('nose_wheel')
self.mapping.add('speedbrake')
self.mapping.add('spoilers')
self._packet_size = struct.calcsize(self.pack_string)
self.set('version', self.FG_NET_FDM_VERSION)
if len(self.values) != self.mapping._nextidx:
raise fgFDMError('Invalid variable list in initialisation')
def packet_size(self):
'''return expected size of FG FDM packets'''
return self._packet_size
def convert(self, value, fromunits, tounits):
'''convert a value from one set of units to another'''
if fromunits == tounits:
return value
if (fromunits,tounits) in self.unitmap:
return value * self.unitmap[(fromunits,tounits)]
if (tounits,fromunits) in self.unitmap:
return value / self.unitmap[(tounits,fromunits)]
raise fgFDMError("unknown unit mapping (%s,%s)" % (fromunits, tounits))
def units(self, varname):
'''return the default units of a variable'''
if not varname in self.mapping.vars:
raise fgFDMError('Unknown variable %s' % varname)
return self.mapping.vars[varname].units
def variables(self):
'''return a list of available variables'''
return sorted(self.mapping.vars.keys(),
key = lambda v : self.mapping.vars[v].index)
def get(self, varname, idx=0, units=None):
'''get a variable value'''
if not varname in self.mapping.vars:
raise fgFDMError('Unknown variable %s' % varname)
if idx >= self.mapping.vars[varname].arraylength:
raise fgFDMError('index of %s beyond end of array idx=%u arraylength=%u' % (
varname, idx, self.mapping.vars[varname].arraylength))
value = self.values[self.mapping.vars[varname].index + idx]
if units:
value = self.convert(value, self.mapping.vars[varname].units, units)
return value
def set(self, varname, value, idx=0, units=None):
'''set a variable value'''
if not varname in self.mapping.vars:
raise fgFDMError('Unknown variable %s' % varname)
if idx >= self.mapping.vars[varname].arraylength:
raise fgFDMError('index of %s beyond end of array idx=%u arraylength=%u' % (
varname, idx, self.mapping.vars[varname].arraylength))
if units:
value = self.convert(value, units, self.mapping.vars[varname].units)
self.values[self.mapping.vars[varname].index + idx] = value
def parse(self, buf):
'''parse a FD FDM buffer'''
try:
t = struct.unpack(self.pack_string, buf)
except struct.error, msg:
raise fgFDMError('unable to parse - %s' % msg)
self.values = list(t)
def pack(self):
'''pack a FD FDM buffer from current values'''
for i in range(len(self.values)):
if math.isnan(self.values[i]):
self.values[i] = 0
return struct.pack(self.pack_string, *self.values)
