I've added some digital filters to the autopilot. They are all low-pass
filters that filter away high frequency signals/noise. There are 4 different
filters:
1. Exponential - The algorithm is essentially the same as the one used in the
fgGetLowPass() function.
2. Double exponential - Two exponential filters in series. This filter has a
"steeper" frequency response curve. It filters "better" than the single
exponential.
3. Moving average - Averages a number of inputs.
4. Noise spike - limits the amount that the output value can change from one
sample to the next.
Filters 1 and 2 are characterised by it's filter-time in seconds. For filter 3
you have to set the number of input samples to average over. For filter 4 you
set the maximum allowed rate of change as [1/s]. Since the sampling interval
(dt) isn't constant we have to calculate the maximum allowed change for every
update.
Example of a double exponential filter with filter time 0.1 seconds, that is
1/0.1 = 10 Hz.
<filter>
<name>pressure-rate-filter</name>
<debug>true</debug>
<type>double-exponential</type>
<input>/autopilot/internal/pressure-rate</input>
<output>/autopilot/internal/filtered-pressure-rate</output>
<filter-time>0.1</filter-time>
</filter>
This would go in the autopilot configuration file.
I've also removed the filtering of the "pressure-rate" helper value, use the
new filters if you want to filter it! ;-)
This patch adds the ability to do a simple scaling of input without having to
add hardcoded helpers. Example:
<reference>
<prop>/autopilot/settings/vertical-speed-fpm</prop>
<scale>0.01667</scale>
</reference>
Add FGPredictor class to xmlauto. Add support for horizontal navigation based
on flight track as opposed to heading. Add crosstrack-error support to nav.
Simplify error adjust calculation for horizontal nav (better interception).
Fixed potential divide by zero that was producing nan issues in the xmlauto
code.
I've done some changes to xmlauto.cxx.
Only calculate the derivate filtering if derivate time Td is greater than
zero. This means that one can set Td=0.0 in the xml file to completely remove
the derivate action. (Setting Td to zero in the current version would lead to
a division by zero and crash.)
Setting the integrator time Ti to zero doesn't make sense, right! I've
modified so that setting Ti to zero results in the integral action being
completely removed.
seem to be fully deterministic in P-only mode. This old simple controller
does what I expect, so it's good for calulating stage #1's of multi-stage
controllers.
controls in the cockpit vs. which wheels they apply to. FlightGear now
sets /controls/gear/brake-left, /controls/gear/brake-right, and
/controls/gear/brake-parking. It should be up to the FDM to sort out
which wheels under which circumstances are affected by these controls
and ultimately what happens to the physical motion of the aircraft.
This has been on my local copy for a while (well tested :-))
It fixes a problem with the auto throttle jumping around needlessly. Adjustments are calculated based on the last calculated autothrottle setting rather than reading the throttle setting from the property tree.
These changes should preserve previous functionality (with the exception of a
couple bug fixes).
Bugs fixed:
- AP no longer resets the error accumulator when switching altitude modes or
just closing the autopilot GUI. It will not be necessary to collect the barf
bags after selecting a new altitude anymore. Makes things much smoother.
- climb_rate calculation in the altitude hold mode included a factor that made
sense for the c172. It is now scaled according to the configuration's target
climb rate.
Additions:
Autothrottle (supports speed control only) is more configurable and accurate.
VerticalSpeed mode added (automatically arms to altitude if flown toward
altitude setting).
Exposed various properties, added new lock properties.
clarity:
nav_radial => nav_target_radial (same as selected, except for a LOC)
nav_heading => nav_reciprocal_radial
nav_magvar => nav_twist (it's not always the same as magvar)
nav_heading_needle_deflection => nav_cdi_deflection
nav_gs_needle_deflection => nav_gs_deflection
Added nav_radial back in, but now it shows the current radial from the
VOR, as one would expect. This value also appears in the
/radios/nav[*]/radials/actual-deg property.
scene management code and organizing it within simgear. My strategy is
to identify the code I want to move, and break it's direct flightgear
dependencies. Then it will be free to move over into the simgear package.
- Moved some property specific code into simgear/props/
- Split out the condition code from fgfs/src/Main/fg_props and put it
in it's own source file in simgear/props/
- Created a scene subdirectory for scenery, model, and material property
related code.
- Moved location.[ch]xx into simgear/scene/model/
- The location and condition code had dependencies on flightgear's global
state (all the globals-> stuff, the flightgear property tree, etc.) SimGear
code can't depend on it so that data has to be passed as parameters to the
functions/methods/constructors.
- This need to pass data as function parameters had a dramatic cascading
effect throughout the FlightGear code.
I modified the files in src/Autopilot to add waypoint capabilities to the telnet port.
'set waypoint <WPT>' will set the next waypoint.
'get waypoint' returns one string which is the list of waypoints.
'set waypoint 0' will delete the next waypoint.
The general idea is to help clean up some aspects of the FDM init and be
able to provide startup conditions in a less ambiguous manner.
Previously, things like positions, orientations, and velocites were set on
"the bus". These had to be read by the FDMs which then were supposed to
initialized themselves to those values and turn write around and start
modifying those values. It was messy and cumbersome.
Now, all the initial fdm conditions are written to a sub-[property-]tree
under /sim/presets/
The values in /sim/presets/ always stay set to what the user has specified.
The user can change these at his/her liesure, and then request a "reset"
which will reset to the new conditions. I don't even want to say how this
worked before. :-)
Now, an script, or gui interface can stage a set of initial conditions while
the sim is running (without disrupting it), and then call "reset" to commit
the change.
People who should worry about all this are FDM writters, and a small few
others who care about over all program structure and flow.
- Removed some old cruft.
- Removed some support for older versions of automake which technically was
correct, but caused the newer automakes to squawk warnings during an
initial sanity check (which isn't done very intelligently.)
NOTE: this fix is technically not correct for older version of automake.
These older version use the variable "INCLUDES" internally and could have
them already set to an important value. That is why we were appending
our values to them. However, newer versions of automake don't set this
value themselves so it is an error to append to a non-existant variable.
We seem to "get away" with overwriting the value on older versions of
automake, but if you have problems, consider upgrading to at least
automake-1.5.
This is a small patch that makes the autopilot work much better with big heavy
airliners as well as the small Cessnas. Of course this doesn't address the
way autopilots should be modeled.
But by making a couple changes the "George" is now capable of landing either a
C172 or a 747 very close to the center line of the runway with a moderate
cross breeze (15-20kt).
The changes:
- Added turn configurability so that things like Max Aileron and Roll can be
configured per aircraft.
- Enhanced localizer routine (NAV mode) to begin lining up the aircraft as soon
as the cone is entered. The former model is adopted for the last 5km of the
approach in order to ensure greater precision (makes a very slight difference).
[float cast added by David Megginson to keep G++ 3.0 happy]
This is a small patch that makes the autopilot work much better with big heavy
airliners as well as the small Cessnas. Of course this doesn't address the
way autopilots should be modeled.
But by making a couple changes the "George" is now capable of landing either a
C172 or a 747 very close to the center line of the runway with a moderate
cross breeze (15-20kt).
The changes:
- Added turn configurability so that things like Max Aileron and Roll can be
configured per aircraft.
- Enhanced localizer routine (NAV mode) to begin lining up the aircraft as soon
as the cone is entered. The former model is adopted for the last 5km of the
approach in order to ensure greater precision (makes a very slight difference).
[float cast added by David Megginson to keep G++ 3.0 happy]
- changed FGSubsystem::update(int) to
FGSubsystem::update(delta_time_sec); the argument is now delta time
in seconds rather than milliseconds
- added FGSubsystem::suspend(), FGSubsystem::suspend(bool),
FGSubsystem::resume(), and FGSubsystem::is_suspended(), all with
default implementations; is_suspended takes account of the master
freeze as well as the subsystem's individual suspended state
- the FDMs now use the delta time argument the same as the rest of
FlightGear; formerly, main.cxx made a special case and passed a
multiloop argument
- FDMs now calculate multiloop internally instead of relying on
main.cxx
There are probably some problems -- I've done basic testing with the
major FDMs and subsystems, but we'll probably need a few weeks to
sniff out bugs.
