439 lines
18 KiB
Text
439 lines
18 KiB
Text
COMMON SETTINGS
|
|
==============================================================================
|
|
|
|
Currently four types of digital filter implementations are supported. They all serve an
|
|
individual purpose or are individual implementations of a specific filter type.
|
|
Each filter implementation uses the same set of basic configuration tags and individual
|
|
configuration elements. These individual elements are described in the section of the
|
|
filter.
|
|
|
|
The InputValue
|
|
==============================================================================
|
|
Each filter has several driving values, like the input value itself, sometimes a reference
|
|
value, a gain value and others. Most of these input values can bei either a constant value
|
|
or the value of a property. They all use the same syntax and will be referred to as InputValue
|
|
in the remaining document.
|
|
|
|
The complete XML syntax for a InputValue is
|
|
|
|
<some-element>
|
|
<condition>
|
|
<!-- any condition as defined in README.conditions -->
|
|
</condition>
|
|
<property>/some/property/name</property>
|
|
<value>0.0</value>
|
|
<scale>1.0</value>
|
|
<offset>0.0</offset>
|
|
<max>infinity</max>
|
|
<min>-infinity<min>
|
|
<abs>false</abs>
|
|
<period>
|
|
<min>-180.0</min>
|
|
<max>-180.0</max>
|
|
</period>
|
|
</some-element>
|
|
|
|
The enclosing element <some-element> is the element defined in each filter, like <input>, <u_min>,
|
|
<reference> etc. These elements will be described later.
|
|
The value of the input is calculated based on the given value, scale and offset as
|
|
value * scale + offset
|
|
and the result is clipped to min/max, if given.
|
|
With the full set of given elements, the InputValue will initialize the named property to the value
|
|
given, reduced by the given offset and reverse scaled by the given scale.
|
|
|
|
Example:
|
|
<input>
|
|
<property>/controls/flight/rudder</property>
|
|
<value>0.0</value>
|
|
<scale>0.5</scale>
|
|
<offset>0.5</offset>
|
|
</input>
|
|
|
|
Will use the property /controls/flight/rudder as the input of the filter. The property will be initialized
|
|
at a value of zero and since the property usually is in the range [-1..+1], the the value of <input> will
|
|
be in the range (-1)*0.5+0.5 to (+1)*0.5+0.5 which is [0..1].
|
|
|
|
The default values for elements not given are:
|
|
<value/> : 0.0
|
|
<scale/> : 1.0
|
|
<offset/>: 0.0
|
|
<property/> : none
|
|
<min/> : unclipped
|
|
<max/> : unclipped
|
|
<abs/> : false
|
|
|
|
Some examples:
|
|
<input>
|
|
<property>/position/altitude-ft</property>
|
|
<scale>0.3048</scale>
|
|
</input>
|
|
Gives the altitude in meters. No initialization of the property is performed, no offset applied.
|
|
|
|
<reference>
|
|
<value>0.0</value>
|
|
</reference>
|
|
A constant reference of zero.
|
|
|
|
A abbreviated method of defining values exist for using a just constant or a property. The above
|
|
example may be written as
|
|
<reference>0.0</reference>
|
|
Or if the reference is defined in a property
|
|
<reference>/some/property/name</reference>
|
|
No initialization, scaling or offsetting is performed here.
|
|
The logic behind this is: If the text node in the element (the text between the opening and closing tag)
|
|
can be converted to a double value, it will be interpreted as a double value. Otherwise the text will
|
|
be interpreted as a property name.
|
|
Examples:
|
|
<reference>3.1415927</reference> - The constant of PI (roughly)
|
|
<reference>/position/altitude-ft</reference> - The property /position/altitude-ft
|
|
<reference>3kings</reference> - The constant 3. The word kings is ignored
|
|
<reference>food4less</reference> - The property food4less
|
|
|
|
The <property> element may also be written as <prop> for backward compatibility.
|
|
|
|
There may be one or more InputValues for the same input of a filter which may be bound to conditions.
|
|
Each InputValue will have its condition checked in the order of InputValues given in the configuration
|
|
file. The first InputValue that returns true for its condition will be evaluated. Chaining a number
|
|
of InputValues with conditions and an unconditioned InputValue works like the C language equivalent
|
|
if( condition ) {
|
|
// compute value of first element
|
|
} else if( condition2 ) {
|
|
// compute value of second element
|
|
} else if( condition3 ) {
|
|
// compute value of third element
|
|
} else {
|
|
// compute value of last element
|
|
}
|
|
|
|
Example: Set the gain to 3.0 if /autopilot/locks/heading equals dg-heading-hold or 2.0 otherwise.
|
|
<digital-filter>
|
|
<gain>
|
|
<condition>
|
|
<equals>
|
|
<property>/autopilot/locks/heading</property>
|
|
<value>dg-heading-hold</value>
|
|
</equals>
|
|
</condition>
|
|
<value>3.0</value>
|
|
<gain>
|
|
<!-- Hint: omit a condition here as a fallthru else condition -->
|
|
</gain>
|
|
<value>2.0</value>
|
|
<gain>
|
|
<digital-filter>
|
|
|
|
If the element <abs> is used and set to the value "true", only the absolute value of the input
|
|
(the positive part) is used for further computations. The abs function is applied after all
|
|
other computations are completed.
|
|
|
|
OutputValue
|
|
==============================================================================
|
|
Each filter drives one to many output properties. No scaling or offsetting is implemented
|
|
for the output value, these should be done in the filter itself.
|
|
The output properties are defined in the <output/> element by adding <property/> elements
|
|
within the <output/> element. For just a single output property, the <property/> element
|
|
may be ommited. For backward compatibility, <property/> may be replaced by <prop/>.
|
|
Nonexisting properties will be created with type double.
|
|
|
|
Example: (Multiple output properties)
|
|
<output>
|
|
<property>/some/output/property</property>
|
|
<property>/some/other/output/property</property>
|
|
<property>/and/another/output/property</property>
|
|
</output>
|
|
|
|
Example: a single output property
|
|
<output>/just/a/single/property</output>
|
|
|
|
Other Common Settings
|
|
==============================================================================
|
|
<name> String The name of the filter. Used for debug purpose.
|
|
Example:
|
|
<name>pressure rate filter</name>
|
|
|
|
<debug> Boolean If true, this filter puts out debug information when updated.
|
|
Example:
|
|
<debug>false</debug>
|
|
|
|
<input> InputValue The input property driving the filter.
|
|
Refer to InputValue for details.
|
|
|
|
<reference> InputValue The reference property for filter that need one.
|
|
Refer to InputValue for details.
|
|
|
|
<output> Complex Each filter can drive one to many output properties.
|
|
Refer to OutputValue for details.
|
|
|
|
<u_min> InputValue This defines the optional minimum and maximum value the output
|
|
<u_max> is clamped to. If neither <u_min> nor <u_max> exists, the output
|
|
is only limited by the internal limit of double precision float computation.
|
|
If either <u_min> or <u_max> is given, clamping is activated. A missing
|
|
min or max value defaults to 0 (zero).
|
|
Note: <u_min> and <u_max> may also occour within a <config> element.
|
|
<min> and <max> may be used as a substitude for the corresponding u_xxx element.
|
|
<period> Complex Define a periodical input or output value. The phase width is defined by the
|
|
child elements <min> and <max> which are of type InputValue
|
|
|
|
Example: Limit the pilot's body temperature to a constant minimum of 36 and a maximum defined in
|
|
/pilots/max-body-temperature-degc, initialized to 40.0
|
|
<u_max>
|
|
<prop>/pilots/max-body-temperature-degc</prop>
|
|
<value>40.0</
|
|
</u_max>
|
|
<min>
|
|
<value>36.0</value>
|
|
</min
|
|
|
|
Implicit definition of the minimum value of 0 (zero) and defining a maximum of 100.0
|
|
<config>
|
|
<u_max>100.0</u_max>
|
|
</config>
|
|
|
|
This defines the input or output as a periodic value with a phase width of 360, like
|
|
the compass rose. Any value reaching the filter's input or leaving the filter at the
|
|
output will be transformed to fit into the given range by adding or substracting one phase
|
|
width of 360. Values of -270, 90 or 450 applied to this periodical element will allways
|
|
result in +90. A value of 630, 270 or -90 will be normalized to -90 in the given example.
|
|
<period>
|
|
<min>-180.0</min>
|
|
<max>180.0</max>
|
|
</period>
|
|
|
|
|
|
<enable> Complex Define a condition to enable or disable the filter. For disabled
|
|
filters, no output computations are performed. Only enabled
|
|
filters fill the output properties. The default for undefined
|
|
conditions is enabled.
|
|
Several way exist to define a condition. The most simple case
|
|
is checking a boolean property. For this, just a <prop> element
|
|
naming this boolean property is needed. The boolean value of the
|
|
named property defines the enabled state of the filter.
|
|
To compare the value of a property with a constant, a <prop> and
|
|
a <value> element define the property name and the value to be
|
|
compared. The filter is enabled, if the value of the property
|
|
equals the given value. A case sensitive string compare is
|
|
performed here.
|
|
To define more complex conditions, a <condition> element may be
|
|
used to define any condition described in README.conditions.
|
|
If a <condition> element is present and if it contains a valid
|
|
condition, this conditions has precedence over a given <prop>/
|
|
<value> condition.
|
|
The child element <honor-passive>, a boolean flag, may be present
|
|
within the <enable> element. If this element is true, the property
|
|
/autopilot/locks/passive-mode is checked and if it is true, the
|
|
filter output is computed, but the output properties are not set.
|
|
The default for honor-passive is false
|
|
Example: Check a boolean property, only compute this filter if gear-down is true and
|
|
/autopilot/locks/passive-mode is false
|
|
<enable>
|
|
<prop>/gear/gear-down</prop>
|
|
<honor-passive>true</honor-passive>
|
|
</enable>
|
|
|
|
Check a property for equality, only compute this filter if the autopilot is locked in heading mode.
|
|
<enable>
|
|
<prop>/autopilot/locks/heading</prop>
|
|
<value>dg-heading-hold</value>
|
|
</enable>
|
|
|
|
Use a complex condition, only compute this filter if the autopilot is serviceable and the lock
|
|
is either dg-heading-hold or nav1-heading-hold
|
|
<enable>
|
|
<condition>
|
|
<property>/autopilo/serviceable</property>
|
|
<or>
|
|
<equals>
|
|
<property>/autopilot/locks/heading</property>
|
|
<value>dg-heading-hold</value>
|
|
</equals>
|
|
<equals>
|
|
<property>/autopilot/locks/heading</property>
|
|
<value>nav1-heading-hold</value>
|
|
</equals>
|
|
</or>
|
|
</condition>
|
|
</enable>
|
|
|
|
INDIVIDUAL FILTER CONFIGURATION
|
|
==============================================================================
|
|
|
|
Digital Filter
|
|
|
|
Six different types of digital filter can be configured inside the autopilot
|
|
configuration file. There are four low-pass filter types and two gain filter
|
|
types.
|
|
|
|
The low-pass filter types are:
|
|
|
|
* Exponential
|
|
* Double exponential
|
|
* Moving average
|
|
* Noise spike filter
|
|
|
|
The gain filter types are:
|
|
|
|
* gain
|
|
* reciprocal
|
|
|
|
To add a digital filter, place a <filter> element under the root element. Next to
|
|
the global configuration elements described above, the following elements configure
|
|
the digital filter:
|
|
<filter-time> InputValue This tag is only applicable for the exponential and
|
|
double-exponential filter types. It controls the bandwidth
|
|
of the filter. The bandwidth in Hz of the filter is:
|
|
1/filter-time. So a low-pass filter with a bandwidth of
|
|
10Hz would have a filter time of 1/10 = 0.1
|
|
|
|
<samples> InputValue This tag only makes sense for the moving-average filter.
|
|
It says how many past samples to average.
|
|
|
|
<max-rate-of-change>
|
|
InputValue This tag is applicable for the noise-spike filter.
|
|
It says how much the value is allowed to change per second.
|
|
|
|
<gain> InputValue This is only applicable to the gain and reciprocal filter types.
|
|
The output for gain filter is computed as input*gain while
|
|
the reciprocal filter computes output as gain/input for input
|
|
values != 0 (zero). Gain may be a constant, a property name
|
|
defined by a <prop> element within the <gain> element or a
|
|
property name initialized to a value by using a <prop> and
|
|
<value> element.
|
|
|
|
Example: a pressure-rate-filter implemented as a double exponential low pass filter
|
|
with a bandwith of 10Hz
|
|
|
|
<filter>
|
|
<name>pressure-rate-filter</name>
|
|
<debug>false</debug>
|
|
<type>double-exponential</type>
|
|
<enable>
|
|
<prop>/autopilot/locks/pressure-rate-filter</prop>
|
|
<value>true</value>
|
|
</enable>
|
|
<input>/autopilot/internal/pressure-rate</input>
|
|
<output>/autopilot/internal/filtered-pressure-rate</output>
|
|
<filter-time>0.1</filter-time>
|
|
</filter>
|
|
|
|
This will filter the pressure-rate property. The output will be to a new
|
|
property called filtered-pressure-rate. You can select any numerical property
|
|
from the property tree. The input property will not be affected by the filter,
|
|
it will stay the same as it would if no filter was configured.
|
|
|
|
Example 2:
|
|
|
|
<filter>
|
|
<name>airspeed elevator-trim gain reciprocal filter</name>
|
|
<debug>false</debug>
|
|
<enable>
|
|
<prop>/autopilot/locks/airspeed-elevator-trim-gain</prop>
|
|
<value>true</value>
|
|
</enable>
|
|
<type>reciprocal</type>
|
|
<gain>
|
|
<prop>/autopilot/settings/elevator-trim-airspeed-reciprocal-gain</prop>
|
|
<value>7</value>
|
|
</gain>
|
|
<input>/velocities/airspeed-kt</input>
|
|
<output>/autopilot/internal/elevator-trim-gain</output>
|
|
<u_min>0.005</u_min>
|
|
<u_max>0.02</u_max>
|
|
</filter>
|
|
|
|
This will use the /velocities/airspeed-kt property to produce a gain factor
|
|
that reduces as airspeed increases. At airspeeds up to 350kt the gain will
|
|
be clamped to 0.02, at 700kt the gain will be 0.01 and at 1400kt the gain will
|
|
be 0.005. The gain will be clamped to 0.005 for airspeeds > 1400kt.
|
|
|
|
The output from this filter could then be used to control the gain in a PID
|
|
controller:
|
|
|
|
<pid-controller>
|
|
<name>Pitch hold</name>
|
|
<debug>false</debug>
|
|
<enable>
|
|
<prop>/autopilot/locks/pitch</prop>
|
|
<value>true</value>
|
|
</enable>
|
|
<input>
|
|
<prop>/orientation/pitch-deg</prop>
|
|
</input>
|
|
<reference>
|
|
<prop>/autopilot/settings/target-pitch-deg</prop>
|
|
</reference>
|
|
<output>
|
|
<prop>/autopilot/internal/target-elevator-trim-norm</prop>
|
|
</output>
|
|
<config>
|
|
<Ts>0.05</Ts>
|
|
<Kp>
|
|
<prop>/autopilot/internal/elevator-trim-gain</prop>
|
|
<value>0.02</value>
|
|
</Kp>
|
|
<beta>1.0</beta>
|
|
<alpha>0.1</alpha>
|
|
<gamma>0.0</gamma>
|
|
<Ti>2.0</Ti>
|
|
<Td>0.2</Td>
|
|
<u_min>-1.0</u_min>
|
|
<u_max>1.0</u_max>
|
|
</config>
|
|
</pid-controller>
|
|
|
|
IMPORTANT NOTE: The <Kp> tag in PID controllers has been revised to operate in
|
|
the same way as the <gain> elements in filters. However, the original format
|
|
of <Kp> will continue to function as before i.e. <Kp>0.02</Kp> will specify a
|
|
fixed and unalterable gain factor, but a warning message will be output.
|
|
|
|
The gain type filter is similar to the reciprocal filter except that the gain
|
|
is applied as a simple factor to the input.
|
|
-------------------------------------------------------------------------------
|
|
Parameters
|
|
|
|
<name> The name of the filter. Give it a sensible name!
|
|
|
|
<debug> If this tag is set to true debugging info will be printed on the
|
|
console.
|
|
|
|
<enable> Encloses the <prop> and <value> tags which are used to enable or
|
|
disable the filter. Instead of the <prop> and <value> tags, a <condition>
|
|
tag may be used to define a condition. Check README.conditions for more
|
|
details about conditions. Defaults to enabled if unspecified.
|
|
|
|
<type> The type of filter. This can be exponential, double-exponential,
|
|
moving-average, noise-spike, gain or reciprocal.
|
|
|
|
<input> The input property to be filtered. This should of course be a
|
|
numerical property, filtering a text string or a boolean value does not make
|
|
sense.
|
|
|
|
<output> The filtered value. You can make up any new property.
|
|
|
|
<u_min> The minimum output value from the filter. Defaults to -infinity.
|
|
|
|
<u_max> The maximum output value from the filter. Defaults to +infinity.
|
|
|
|
These are the tags that are applicable to all filter types. The following tags
|
|
are filter specific.
|
|
|
|
<filter-time> This tag is only applicable for the exponential and
|
|
double-exponential filter types. It controls the bandwidth of the filter. The
|
|
bandwidth in Hz of the filter is: 1/filter-time. So a low-pass filter with a
|
|
bandwidth of 10Hz would have a filter time of 1/10 = 0.1
|
|
|
|
<samples> This tag only makes sense for the moving-average filter. It says how
|
|
many past samples to average.
|
|
|
|
<max-rate-of-change> This tag is applicable for the noise-spike filter. Is
|
|
says how much the value is allowed to change per second.
|
|
|
|
<gain> This, and it's enclosed <prop> and <value> tags, are only applicable to
|
|
the gain and reciprocal filter types. The <prop> tag specifies a property node
|
|
to hold the gain value and the <value> tag specifies an initial default value.
|
|
The gain defaults to 1.0 if unspecified.
|
|
|
|
The output from the gain filter type is: input * gain.
|
|
The output from the reciprocal filter type is: gain / input.
|
|
|
|
The gain can be changed during run-time by updating the value in the property
|
|
node.
|