Module gps mod SGNQF_v 0.1

Overview

This GPS related stream module is devoted to positioning measures filtering using quality informations provided by the device itself. Information on satellite count, horizontal dilution of position and measure fix are considered to determine measure quality. Measures that are below the defined threshold are simply removed.

Module nomenclature

This stream module waits a physical stream and an integer unitary stream as input. Typically, this module is used just after GPS data extraction in order to remove bad signals due to satellite loss caused by objets, buildings or tunnels. A physical stream and an integer unitary stream are given as module output. This following image gives a sketch of the module nomenclature :

The output physical stream has to carry GPS geopositions when the unitary stream has to contains the compacted informations on GPS signal quality. The quality informations of kept GPS measures are preserved for subsequent modules.

Module interface

This section gives a summary of the module interface in terms of streams and devices. The order of devices and streams is given as waited by the module. The devices interface is given by :

Device( Physical ) GPS reciever

The stream input interface is :

stream( Physical        | GPS ) Geopositions
stream( Integer unitary | GPS ) Signal quality

and the stream output interface is :

stream( Physical        | GPS ) Filtered geopositions
stream( Integer unitary | GPS ) Filtered signal quality

The two input streams are attached as well as the two output streams.

Module operation

The module reads three information about each GPS measure and determine if measure has to be kept or removed. The first considered information is the measure fix. The following table gives the filtering decision according to fix value and its description :

Removed   0    Invalid
Kept      1    GPS fix (SPS)
Kept      2    DGPS fix
Kept      3    PPS fix
Kept      4    Real Time Kinematic
Kept      5    Float RTK
Removed   6    Estimated (dead reckoning) (2.3 feature)
Removed   7    Manual input mode
Removed   8    Simulation mode

After fix filtering, the number of satellites used for the measure is considered. The filter reject every measure that was performed using less than six satellites.

Finally, the horizontal dilution of position (HDOP) is considered. Each measure that comes with a dilution greater than 4.00 are removed by the filter.