Re: QT block to plot datapoints as they come in and keep history

[Nate Temple]

Hi Luke,

Checkout the gr-radar OOT, it has a few QT GUI plots that may work for this, or at least it will give an example to start with, if you choose to make your own plot widget.

Regards,
Nate Temple

On Wed, Dec 18, 2019 at 1:31 PM Lukas Haase <address@hidden> wrote:

Hello,

I have a block which computes a distance and outputs this distance regularly (10x per second) via a message.

I am looking for a way to plot this distance over time: Basically, whenever a new update comes in, it should show this value while keeping a certain amount of past samples so that the distance can be seen over time.

I played with the QT GUI Time Sink for quite some time (playing with sample rate, update period, sending a vector of same numbers in the message or sending just a vector with one element). The value updates but it only shows the point at t=0 which moves up and down on the y-axis ... but I do not get the history over time.

I also tried implementing a "message-to-sample" converter that works like this:

def incoming_msg(self, msg): # whenever new message comes in, update our state
   if pmt.is_f32vector(msg):
      dist = pmt.to_python(msg)
      self.distance = dist[0]

def work(self, input_items, output_items): # this is a source block
    output_items[0][:] = self.distance # for each block, just output constant signal
    return len(output_items[0])

Now I see a constant line that shifts up and down regularly, but still no distance-vs-time plot.

Any suggestions?

Thanks,
Luke