WSF_DIRECTION_FINDER_PROCESSOR

processor WSF_DIRECTION_FINDER_PROCESSOR

Derives From: WSF_LINKED_PROCESSOR

processor <name> WSF_DIRECTION_FINDER_PROCESSOR
   ... WSF_LINKED_PROCESSOR Commands ...
   fuse_all_measurements | fuse_all_collects
   measurement_replacement_interval | collect_replacement_interval
   maximum_expected_error
   use_truth_altitude
   filter
   filter_bypass
   maximum_time_difference
   minimum_baseline_distance
   test
end_processor

Overview

WSF_DIRECTION_FINDER_PROCESSOR is a specialized processor that is used to fuse multiple bearing-only tracks (e.g., from one or more passive systems). This function is somewhat different from the standard WSF “default” fusion. Usually track data are filtered first, then fused. In this case the raw bearing track data must be fused to form location and location error data, then the filtering takes place. The products of the direction-finder processor are fused-filtered tracks with valid, triangulated target location.

This filtering is necessary in order to reduce the triangulation error to actionable values. As pairs of reports are run through the triangulation algorithm, the error in the location goes down as the square root of the number of pairs accumulated.

Typically this processor would be the consumer of track reports from a bearing-only sensor. Therefore, the sensor would be linked with the direction finder processor as follows:

processor direction-finder WSF_DIRECTION_FINDER_PROCESSOR
end_processor

sensor passive_sensor WSF_PASSIVE_SENSOR
   internal_link direction-finder
   ...
end_sensor

The outputs of the direction-finder processor are tracks containing valid target position data. Typically, it would be linked with a WSF_TRACK_PROCESSOR or a communications link to an external fusion node. For example:

processor direction-finder WSF_DIRECTION_FINDER_PROCESSOR
   processor track
   processor share
end_processor

processor track WSF_TRACK_PROCESSOR
end_processor

processor share WSF_LINKED_PROCESSOR
   report_to commander via datalink
end_processor

comm datalink WSF_COMM_TRANSCEIVER
end_comm

Commands

fuse_all_measurements

fuse_all_collects <boolean-value>

If enabled, all measurements for a given target will be used for direction finding. Otherwise if the expected value of the location error, after the pair are utilized, is greater than the current value, the pair will not be fused.

Default: disable

measurement_replacement_interval

collect_replacement_interval <time-value>

Specifies a time interval after which an existing measurement that has not been used for direction finding, will be updated with a more recent measurement.

Default: 1.0e+12 (Infinite)

maximum_expected_error <length-value>

Specifies a maximum value in a single dimension, that the expected direction-finding error value should not exceed.

Default: 100000 m

use_truth_altitude <boolean-value>

Specifies that the actual altitude should be used when reporting the locations of air targets.

Default: disabled

filter … end_filter

Associates a filter type with this processor. All incoming tracks of that have no filter, will be assigned this type. If this command isn’t indicated, a WsfKalmanFilter type will be used.

Default: WsfKalmanFilter w/zero process noise

filter_bypass <flag>

Allows bypassing the filter, such that the output will be the ‘measurement’, which is just the intersection point from a successful triangulation.

Default: filter enabled

minimum_baseline_distance <length-value>

Specifies the minimum distance between origin locations of pairs of measurements being fused.

Default: 10 km

maximum_time_difference <time-value>

Specifies the maximum time difference allowed between measurements. Measurements that exceed this time difference, will not be fused. This helps reduce errors when the targets are moving. If this field is not included, there is no maximum time difference - all pairs will be fused, assuming all other things being equal.

Default: 1.0e+12 (Infinite)

test <boolean-value>

Enable output of diagnostic messages and a WsfDraw-based representation of each direction-finding solution. Diagnostic messages are output when candidate direction finding solutions fail due to the following:

• Angle threshold test failure: The interior angle formed by the two candidate target vectors is less than five times the maximum expected azimuth error of the two measurements. This test rejects solutions with very large uncertainties in range.

• Baseline distance test failure: The distance between the origin of the two measurement positions is less than that specified by the minimum_baseline_distance command.

• Bearing lines divergence failure: The lines of bearing of the two measurements are divergent in the direction of the target (i.e., they intersect in the opposite direction from the target).

• Maximum expected range error failure: The computed expected range error exceeded the value specified with the maximum_expected_error input.

WsfDraw-based visualization of solutions displays green lines along the track direction, red lines to indicate the extents of expected bearing errors, blue lines and points to show the extent of the errors of the computed 3D solutions, and a point to indicate the computed target location.