[Discuss-gnuradio] gr-qtgui Waterfall Time Axis

[Garver, Paul W]

I have some large spectrum records and I would like to use GR for analysis in a 
a sort of "off-line" mode.  I want to visualize the data using the spectrogram 
and then identify subsets of interesting features (e.g. WiFi Packets in 2.4 
GHz) by frequency and time coordinates.  Essentially, I want to know what index 
in the file certain features correspond with so I can save them as separate 
files.  To this end, I've found gr_spectrogram_plot very handy, but it doesn't 
quite do what I want because the y-axis which displays time isn't showing up 
correctly.  My y-axis is always 0.0, and the cursor highlight also reads 0.0 
(although the frequency is correct).  However, the qt spectrogram appears to 
have correct time information when I make a simple file source -> qt 
spectrogram sink.  

I'd like to fix this issue so I've been pouring over the code in gr-qtgui.  I 
don't have much experience with QWT or Python GUIs in general.  From what I can 
tell, there are methods for frequency axis and intensity scaling, but not time. 
 Is this true or am I missing something in the API?  The historyExtent 
parameter in the WaterfallData constructor appears to get hardcoded to 200 in 
WaterfallDisplayPlot.cc (gr-qtgui/lib).  It would also be nice to toggle 
between the time and sample number.

I'm happy to do the work to implement this.  Could someone point me in the 
right direction here?  Thanks!

PWG