The generic communication protocol for FlightGear provides a powerfull way
of adding a simple ASCII based output only protocol, just by defining an
XML encoded configuration file and placing it in the $FG_ROOT/data/Protocols
directory.

The definition of the protocol consists of variable separators, line separators,
and chuncks of text.

Each chunck defines:

<name>		for ease of use
<node>		the property tree node which provides the data
<type>		the value type (needed for formatting)
<format>	defines the actual piece of text which should be sent.
		it can include formatting options like:
				<type>
			%s	string
			%i	integer	(default)
			%f	float

<factor>	an optionale multiplication factor which can be used for
		unit conversion. (for example, radians to degrees).
<offset>	an optional offset which can be used for unit conversion.
		(for example, degrees Celsius to degrees Fahrenheit).


The output section also could define the variable separator and line separator.

The separators can be either a control character such as a tab or newline, or a
user specified string or other single charachter. The currently supported
control charachters are:

<var_separator>:
<line_separator>:
Name		Charachter

newline		'\n'
tab		'\t'
formfeed	'\f'
carriagereturn	'\r'
verticaltab	'\v'

any other charachters just need to be added to "Network/generic.cxx"

The var_separator is placed between each variable, while the line_separator is
placed at the end of each lot of variables.


A simple protocol configuration file then could look something like the
following:

<?xml version="1.0"?>

<PropertyList>
 <output>

   <line_separator>newline</line_separator>
   <var_separator>newline</var_separator>

   <chunk>
    <name>speed</name>
    <format>V=%d</format>
    <node>/velocities/airspeed-kt</node>
   </chunk>

   <chunk>
    <name>heading (rad)</name>
    <format>H=%02d</format>
    <node>/orientation/heading-deg</node>
    <factor>57.29578</factor>  <!-- degrees to radians -->
   </chunk>

   <chunk>
    <name>pitch angle (deg)</name>
    <format>P=%05.1f</format>
    <type>float</type>
    <node>/orientation/pitch-deg</node>
   </chunk>

 </output>
</PropertyList>