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Qdf

A Qt application using DFLib to manage direction finding activities and plot using Google Earth and APRS

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Introducing qDF, an application for computing radio-direction finding solutions from bearings-only measurements.

qDF is a simple Qt GUI application that allows input of data from radio direction finding (RDF) activities, computation of target location using DFLib, display of RDF data in Google Earth, and publication of RDF data (including solutions) to APRS.

How do I get qDF?

qDF is available only in source code form, and has DFLib as a prerequisite. First, download and install DFLib from its repository. Install a full set of Qt development packages for your operating system. Then Download the latest source code of qDF using the ".tar.gz" or ".zip" and build it according to the directions in the next section.

No pre-built binary packages of qDF are provided. This is a source-code-only release.

How do I build qDF?

Once you have downloaded and installed all the prerequisites for building (that is, DFLib (with its own prerequisites)and Qt 4 or Qt 5), building qDF is simple. The explanation here is for Linux systems. qDF has been built and tested on FreeBSD, Mac OS X, and even Windows, but those systems require more work and are not yet documented here (they will be eventually).

The qDF tarball from the link above will have the name "tvrusso-qDF-<hexnumber>.tar.gz, where the hexadecimal number representing the current state of the GitHub repository has been filled in where I've written "<hexnumber>". Unpack and build the code as follows (substituting the correct number where "<hexnumber>" appears):


          tar xzf tvrusso-qDF-<hexnumber>.tar.gz

          cd tvrusso-qDF-<hexnumber>

          mkdir build

          cd build

          qmake ../qDF.pro

          make

If you've got all the prerequisites installed correctly, this should just work, and will create an executable in the "build" directory named "qDF."

How do I run qDF?

On a Linux or FreeBSD system, just execute the "qDF" program you just created. There are additional tricks to finding and running the qDF program built on OS X that depend on what package add-on system you're using.

On start-up, qDF will open its main window, which consists of a panel displaying how many DF reports are currently entered and marked valid, a list of target position estimates (initially "Not Available", of course, since there's been no input), a panel showing the list of reports in summary format, and a panel meant to show outgoing APRS traffic. TBD: insert screenshot

TBD: beef this up. There are settings you must initialize under the "Edit-<Settings..." menu. These include information about your current magnetic declination and preferred coordinate system, information used to control the "Fix Cut Average" computation, and information about your APRS server (including whether or not to use one).

Enter DF reports by choosing "Report-<New Report". Give each report a unique name, enter the receiver's location in latitude/longitude (with correct datum), and the magnetic bearing reported by the receiver. Set the equipment type and "fix quality", then click "OK". TBD: Insert screenshot. As you build up a collection of reports, the various solutions will start showing up in the main window.

As you add DF reports, a file called "qDF_GE_data.kml" in the current working directory will be populated with "Keyhole Markup Language" data that Google Earth can use to display the data. A second KML file called "qDF_GE.kml" is the one you should actually open in Google Earth --- this file instructs Google Earth to re-read the other data file frequently, so your display is kept in sync with your data.

The data displayed includes:

The locations of DF receivers reporting.
Bearing lines from those receivers in the direction the transmitter was heard.
Target location estimates (Fix Cut Average, Least Squares Fix, Stansfield Fix, Maximum Likelihood Fix). See DFLib documentation for details of how these fixes are computed and for further reading.
Confidence intervals for the Stansfield and Maximum Likelihood fixes. These rings indication the 50%, 75%, and 95% confidence range for the fix type.

In Google Earth, receivers, fixes, and confidence rings are all stored in separate "folders" so that you can turn display of those items on or off to declutter your map. TBD: Screenshot!

In addition, if you have configured qDF to publish data to APRS, the same data will be sent to an APRS program of your choice (via UDP datagrams, supported by only a few varieties of APRS client). This should get your data displayed on the APRS map for your client, and if configured correctly, the same data should be transmitted to the APRS RF network. For a search and rescue operation, having this data transmitted to the network is useful so that all participants in the DF activity receive all the data from other DFers as well as the target location estimates.

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