82 lines
2.8 KiB
Text
82 lines
2.8 KiB
Text
Logging in FlightGear
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---------------------
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[Note: JSBSim also has its own independent logging facilities, which
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are not discussed here.]
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FlightGear can log any property values at any interval to one or more
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CSV files (which can be read and graphed using spreadsheets like
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Gnumeric or Excel). Logging is defined in the '/logging' subbranch of
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the main property tree; under '/logging', each '/log' subbranch
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defines a separate log with its own output file and interval. Here is
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a simple example that logs the rudder and aileron settings every
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second (1000ms) to the file steering.csv, using a comma (the default,
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anyway) as the field delimiter:
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<logging>
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<log>
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<filename>steering.csv</filename>
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<interval-ms>1000</interval-ms>
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<delimiter>,</delimiter>
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<entry>
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<title>Rudder</title>
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<property>/controls/rudder</property>
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</entry>
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<entry>
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<title>Ailerons</title>
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<property>/controls/aileron</property>
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</entry>
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</log>
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</logging>
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Each 'log' subbranch contains an optional 'filename' property
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(defaults to "fg_log.csv"), an optional 'delimiter' property (defaults
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to a comma), an optional 'interval-ms' property (defaults to 0, which
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logs every frame), and a series of 'entry' subbranches. The
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'delimiter' property uses only the first character of the property
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value as the delimiter. Note that the logger does no escaping, so you
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must choose a delimiter that will not appear in the property values
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(that's not hard, since most of the values are numeric, but watch for
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commas in the titles).
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Each 'entry' subbranch contains a 'property' property specifying the
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name of the property to be logged, and an optional 'title' property
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specifying the title to use in the CSV file (defaults to the full path
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of the property). The elapsed time in milliseconds since the start of
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the simulation is always included as the first entry with the title
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"Time", so there is no need to include it explicitly.
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Here's a sample of the logging output for the above log:
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Time,Rudder,Ailerons
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6522,0.000000,0.000000
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7668,-0.000000,0.000000
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8702,-0.000000,0.000000
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9705,-0.000000,0.000000
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10784,-0.000000,0.000000
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11792,-0.000000,0.000000
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12808,-0.000000,-0.210000
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13826,-0.000000,-0.344000
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14881,-0.000000,-0.066000
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15901,-0.000000,-0.806000
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16943,-0.000000,-0.936000
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17965,-0.000000,-0.534000
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19013,-0.000000,-0.294000
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20044,-0.000000,0.270000
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21090,-0.000000,-1.000000
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22097,-0.000000,-0.168000
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Note that the requested interval is only a minimum; most of the time,
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the actual interval is slightly longer than the requested one.
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The easiest way for an end-user to define logs is to put the log in a
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separate XML file (usually under the user's home directory), then
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refer to it using the --config option, like this:
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fgfs --config=log-config.xml
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The output log files are always relative to the current directory.
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--
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David Megginson, 2002-03-12
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