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[Discuss-gnuradio] Markers or tag support for QT GUI Vector Sink


From: Ben Winstead
Subject: [Discuss-gnuradio] Markers or tag support for QT GUI Vector Sink
Date: Tue, 15 May 2018 17:28:54 -0400

Hi all,

I'm trying figure out if there is a way to plot markers at certain positions in a QT GUI Vector Sink plot.  I'm providing FFT magnitude results as vectors of length equal to the FFT size.  I then want to add one or more markers at certain peaks along that vector that is plotted, but I can't find a way to do that.

If I were supplying the fft results as a stream, I could add tags at the positions where the peaks occur.  I could make that work on a QT GUI Time plot with a tagged stream input with triggering based on a "packet_len" tag, but then I lose the control of my X axis labeling and it would always display a nuisance "packet_len" tag at the beginning of the plot in addition to the desired tags that I would add.

If I understand correctly, tags cannot be assigned to a specific element in a vector because tags are assigned to a specific item number and a vector is considered a single item.  Therefore, it's probably not feasible to add tags to the Vector Sink block with the existing tag concept.  However, might you be able to add a tag on each vector that contains some structure that the Vector Sink could be configured to recognize?  The tag in this case would contain all of the x-y positions (and associated labels) of markers to be plotted for that vector item.

Regards,
Ben Winstead


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